This truck has the knocking sound since the day I bought it. Since then I replaced several things. Here's the chronological order of the events:
1) About 1 year ago, I replaced the flexplate and the torque converter, hoping that it will help. Not sure whether it helped indeed - the transmission lost the 3 and 4 gears about one week after the replacement. I did not had enough time to notice any changes... I think the mechanic that did the job did not put enough ATF and I did not check that...
2) I bough another used transmission and paid another mechanic to install it. The "new" transmission came with its torque converter and I told the mechanic to put that transmission together with its torque converter I am not sure what he did but the same noise remained after the transmission swap. Also, there was a problem with the converter lockup after the swap - the shudder; the problem was solved by deleting the PWM by HPTuner. Since then, the transmission did about 30k km, shifts OK. However, the knocking noise is annoying. It is not that loud; sometimes I can barely hear it. The noise becomes louder when the engine is getting hot.
3) I was not sure whether the knock is coming from the transmission or from the engine, and did a test: I disconnected the torque converter from the flexplate. The noise has gone. This confirms that the noise is coming from the transmission.
It is a second transmission, another flexplate, supposed to be another torque converter but the noise is still there and I don't have any reasonable explanation why. I think the second mechanic swapped the transmissions but left the old torque converter. That converter probably has some problem and makes that noise. So, I am almost ready to remove the transmission and replace the torque converter. I have a new converter - the same that I bought from eBay store (Cyclone Transmissions) and asked the mechanic to put on the truck together with a new flexplate. I think this converter is good. The question is whether I need to replace the pump. basically, I have several options:
1) to drive the truck as is until the transmission dies;
2) try to replace the torque converter and the pump;
3) put another used transmission;
4) pay to the shop to do an overhaul of the transmission.
So, I am not sure what to do. The budget is somewhat tight so I don't want to rebuilt the transmission.