Help diagnosing an engine rattle?

[Shdwdrgn]

Don't worry, I won't leave this thread with such a horrible question! So basically the symptoms are that when the engine is cold, I get a rattle from the engine when taking off from a stop. It sees to calm down while coasting down the road or once the engine warms up, and really only seems to be noticeable first thing in the morning. After that it runs smooth as can be. The best way I can describe the sound is similar to something flapping in the wind when you're going down the highway at high speed, but I don't actually feel any issues to suggest a drive train issue? It's definitely tied to the engine speed though and even when cold it goes away above around 3000rpm.

So my first thought here was the fan clutch, but after checking I realized the water pump bearings were shot and I replaced that today (and thankfully had no issues getting the fan clutch nut loose this time) and now both the pump and clutch feel good and tight again. However when I took it out for a test drive, I still am getting a little bit of that rattle -- since it's already been driven today, I'm not sure yet if the noise is still as bad?

One thing I remember reading a lot of people mentioning years ago is problems with an engine mount coming loose or breaking. I have no idea what that would sound like, and if this were the case then I would think I would hear the problem again when I gun the engine on the highway? At this point I'm just grasping at straws though, there's nothing obviously loose in the engine compartment but it's not like I went through and touched everything.

Anyway, I don't know if anyone has suggestions on what I should check next. I'll be getting back under the hood again soon because I'm still running cold, so it must be time to replace the thermostat again, I'm just out of ideas...

 

[mrrsm]

At First Blush....I'm suspecting that you may have a Cracked Flex-Plate. In the past, many other members (and Lurkers) have helped themselves in running strange sounds to ground using their Cell Phones to record a series of *Takes* on a single Video that shows them opening the Engine Hood and dividing up the areas above the Idling Engine( Parking Brake SET- Wheels CHOCKED) ... then to the Left, the Right, the Front upper areas and gradually lowering the Camera below the Wheel Wells, then the Front Bumper... and finally... capture the sounds emanating on either side of the Driver's and Passenger Front Doors while slipping the camera underneath the area adjacent to the mate up at the back of the Engine to the Bell Housing-4L60E Transmission..

After you've posted up your Video(s) to YouTube and then linked back here... some of our Folks might recognize what is actually going on. Everything from having any of the Three Torque Converter Bolts coming loose to an actual Fractured Flex- Plates have been discovered under there over the years. On one or two other occasions, fractured Ceramic Cores inside of the CAT Stainless Steel Canister have "rung like a bell" during engine idling and made things even more confusing.

The latter problem is easily diagnosed by laying down a Big Section of Cardboard underneath the Passenger Side of the SUV and using a Dead Blow Hammer to Very Lightly *Tap-Tap-Tap* along the bottom areas of the CAT Can. If you can hear the sound of "Loose Change dropping into a Ceramic Bowl" -sort of sound... then the CAT would need replacing.

In the mean time... checking out Videos like THESE might help with narrowing down the cause and origin of all that RACKET:

So... What Causes the Flex-Plate to CRACK?

When the GM 4.2L LL8 Engine is Factory Fresh, The Engine Main Bearing have been installed with the Thrust Bearing in the 5Th Position... meant to RESTRICT the Forward and Aft Hunting motion of the Crankshaft as it normally is supposed to move Back and Forth within a very small margin of motion. If the Thrust Bearing has become Worn Out... the Motion of the Crankshaft In and Out tends to BEND the inner portion of the Flex Plate Bolt On section much like a Cone Shape.

Another issue is that if a Harmonic Balancer is either mis-installed or becomes loose enough to slide and move in an out on the nose of the Crankshaft...the same outcome will occur. In time, these repeated Excessive Flexing movements become well beyond its design specs and will cause that Rear Crank Bolt- Up section to Work Harden that portion of the Flex-Plate and eventually Crystallize the Metal and CRACK that area completely loose. To give you an idea of just how much motion is possible observe THIS situation in progress:

 

[Shdwdrgn]

One thing just to clarify... this noise is only happening while under load, like when I take off from the light. There are no unusual sounds when it's sitting there idling or even from the easy job of backing out of my driveway. And all problems go away within the first few minutes of driving.

 

[mrrsm]

JIK you have not looked everything over yet... Check Underneath the Vehicle and see if something like a Plastic Garbage Bag or its *ilk* may have become entangled up under there.

 

[Mooseman]

I dunno about a cracked flexplate. That would make noise all the time.

Is it possible the noise is from a cracked exhaust manifold or leak? That seems the most plausible. As the manifold heats up, the metal would expand and close the crack or leak, which would be why the noise stops once hot.

As far as an engine mount, that only causes a 10Hz vibration while stopped in drive. No noise unless it's rattling something inside the truck and it doesn't go away when warm.

 

[Mike534x]

I agree with @Mooseman. I'd cast my vote into saying its a cracked exhaust manifold, it sure sounds like given when you do hear the noise and the duration its around until it quiets down, or goes away.

Best bet would be to see if you can remove the heatshield (it may, or may not break due to years of heating/cooling cycles) or bend it back enough to inspect the manifold. In theory, if you have a bright LED flashlight, and an inspection mirror you should be able to see the faint outlines of a crack or spiderweb looking crack snaking its way around the headers, or on the backside facing the engine block (the mirror comes in handy here).

When my Envoy had 2 of the exhaust manifold bolts snap on the passenger side (granted its a V8), it sounded like it had a metallic ticking sound at idle, and worse under load until the engine was up to operating temp and the manifold was hot enough to close the gap a bit from where it leaking past the heads.

 

[Shdwdrgn]

Thanks everyone for the suggestions so far, any easy things to look for regarding a cracked exhaust? Is that something you feel around for a hot air leak, or would the crack be easily visible?

I drove around the block after lunch today, and the noise does appears to be greatly reduced from what I've been hearing the past week. Hopefully that's a good sign that the worst of the noise *was* actually coming from the water pump, but there is still a lower-intensity noise at first that sounds the same as what I heard before. What I saw today is that the sound only seems to happen between about 2000-3000rpm, with the worst centered right at 2500.

Basically the noise that has been getting worse, and was extremely bad on Thursday (like I almost turned around because I could feel the vibration)... THAT intensity appears to have been resolved with the water pump, but I should know for sure when I head to work in the morning.

So if the sound I'm hearing is the sound of worn bearing rattling around, I'm wondering if maybe something else is also starting to go? The power steering pump was just replaced a few years ago so it should be good, but the water pump and alternator are both OEM with over 180k miles. This is the first vehicle I've owned with a serpentine belt, is there anything in that train I should look for? (Guess yesterday would have been the time for that with the fan should and everything out of the way -- oh well!)

If I don't experience the really bad noise from last week again then I'll feel a lot better, at least what I'm hearing now doesn't sound like the engine is about to blow apart.

 

[Mooseman]

You can take the belt off and spin each individual component by hand to find any noise. It could be a bearing in an idler pulley or alternator.

 

[mrrsm]

Just as you suspect... The one other Accessory that can "Rattle" is the Fan Blade Shroud from a Bad Water Pump Bearing... So... Check Out @Matt's Thread for the WP R&R HERE:

How to replace the water pump

Total time, about an hour. On the OS someone claimed to have done it in 30 minutes, but it took me about an hour from getting everything out to having everything packed away. Make sure the engine is COMPLETELY cool before doing this. Best bet is to do it first thing in the morning. Remove the...

gmtnation.com

Post #15 in the Linked Thread tells a comprehensive (and Pictorial) story in support of @Mooseman 's and @Mike534x 's impressions regarding a Cracked Cast Iron Exhaust Manifold *Huffing and Puffing* through the opening until it gets HOT enough to "Seal The Breach" so to speak:




IF the IM is Cracked and an R&R is in order, You will NEED Longer Exhaust Manifold Flange Fasteners for the Dorman IM...Like THESE:

the exhaust manifold crowd... :-(

so, my "replaced under extended warranty" exhaust manifold cracked again... basically about 4 years after the replacement. Of course, it is unlikely that GM or the dealer will do much for me. Not sure that I am willing to spend coin on them as opposed to maybe a third party shop. I suspect...

gmtnation.com

The Crux of the cause and origin of Cracked Exhaust Manifolds and Broken Exhaust Manifold Flange Bolts is having BAD MOTOR MOUNTS. The collapse of the Gel Filled Mounts will allow EXCESSIVE SIDE ROLL of the Engine as as the Block reacts and... following Newton's Third Law of Motion "For EVERY Action their is an Opposite and Equal Reaction" jerking the Block loosely in the opposite direction of Crankshaft Rotation,. This results is what you can see in the Linked Images above... Flexing the Cast Iron sub-pipes junction and eventually Cracking them Open like Hen's Eggs.

THIS Video describes ONE Method of performing this R&R... There ARE several ways to attack this problem that others may be more familiar with. Also ...Spend the MONEY on the ACDelco Motor Mounts... and save the Headache of using Chinese Knock-Offs that may FAIL very soon after the R&R:

 

[Realism]

JIK you have not looked everything over yet... Check Underneath the Vehicle and see if something like a Plastic Garbage Bag or its *ilk* may have become entangled up under there.

was going to say. has he checked for zip ties around the drive shaft

 

[Realism]

Thanks everyone for the suggestions so far, any easy things to look for regarding a cracked exhaust? Is that something you feel around for a hot air leak, or would the crack be easily visible?

I drove around the block after lunch today, and the noise does appears to be greatly reduced from what I've been hearing the past week. Hopefully that's a good sign that the worst of the noise *was* actually coming from the water pump, but there is still a lower-intensity noise at first that sounds the same as what I heard before. What I saw today is that the sound only seems to happen between about 2000-3000rpm, with the worst centered right at 2500.

Basically the noise that has been getting worse, and was extremely bad on Thursday (like I almost turned around because I could feel the vibration)... THAT intensity appears to have been resolved with the water pump, but I should know for sure when I head to work in the morning.

So if the sound I'm hearing is the sound of worn bearing rattling around, I'm wondering if maybe something else is also starting to go? The power steering pump was just replaced a few years ago so it should be good, but the water pump and alternator are both OEM with over 180k miles. This is the first vehicle I've owned with a serpentine belt, is there anything in that train I should look for? (Guess yesterday would have been the time for that with the fan should and everything out of the way -- oh well!)

If I don't experience the really bad noise from last week again then I'll feel a lot better, at least what I'm hearing now doesn't sound like the engine is about to blow apart.

Have you tried reproducing the sound while just in park by ramping up rpm?
It does sound like something is out of balance. Mrrsm does point out a great possibility. If your fan clutch is engaging at some point and its a little off balance you could be just knicking or causing the shroud to vibrate. Vibrating plastic can have an interesting bag like whoop whip sound. And since our fan clutches are an EV clutch, it does take some time for things to work out, so it works worse on cold start

 

[Shdwdrgn]

I unfortunately haven't had any time to get back to it again. I've never noticed the issue except when in gear but it could just be that there's not enough load to make it loud enough to hear? The other thing I've been trying to watch for is to see if there is an associated vibration with the noise. It's one of those things that I *expect* there to be a vibration with, so I'm not quite sure if my brain isn't fooling me. And of course most of the time when I notice it, is when I'm rushing off to work and paying more attention to traffic.

So yeah, I'm still not completely certain of what's going on, but I'm trying to narrow it down...

 

[mrrsm]

It is rare... but having a Clogged Torque Converter (Friction Platter Debris) that can occasionally become Out Of Balance or by having a Failing Transmission Fluid Pump can manifest with Vibrations that will only be in evidence when the 4L60E Transmission is In Gear and when the Engine is at Idle conditions.

 

[Shdwdrgn]

@mrrsm Thanks but this only seems to be occurring for the first few minutes while the engine is cold, and while under load like pulling away from a stop light. It still idles nice and smooth, and by the time I hit the highway it is warmed up enough that there is no noticeable issue even under heavy acceleration.