Originally Posted by tx_shooter

I had a similar strange metallic knocking that only happened when in gear. It ended up being the exhaust system contacting the transmission. I could not reproduce the sound when sitting in Park; but ended up having my wife hold the 4R in Drive while I listened from the side. Once I replaced the exhaust system the rattle and knocking stopped. Apparently the mount rubbers were broken down allowing for extra movement and the muffler had a large amount of rusted internals allowing for a rattle or knocking depending on RPMs.

Originally Posted by SigSaucer

I'm reviving this to see if anyone figured out exactly what the issue was?

Was this the noise, guys?

https://www.youtube.com/watch?v=zE6zf1XVX3o&feature=youtu.be

* Noise only occurs in gear once warm

* On the first start up, rarely, the noise does not occur until you goose the gas a bit in gear with your foot on the brake. This starts the noise occurring and it won't go away after it starts.

* My flexplate and bolts looked perfectly fine, bolts were tight.

The problem is not caused by any of the following:

1) The rod bearings (replaced mine, no change).

2) Crankshaft end play (measured mine, well within Toyota spec)

3) The water pump, timing belt, timing belt tensioner, timing belt tensioner pulley, or timing belt idler pulleys (replaced mine, no change).

4) The AC compressor pulley bearing (replaced mine, no change)

5) The V belt tensioner pulley (replaced mine, no change)

6) The V belts (replaced mine, no change)

Originally Posted by SigSaucer

Can anyone else verify that they have the same knocking noise as I posted in this video? https://www.youtube.com/watch?v=zE6zf1XVX3o&feature=youtu.be

Here's more information: the noise "goes away" when ANY ONE OR MORE of the three accessory drive belts are removed.

For example, if I remove only the power steering belt, the noise goes away. If I put the power steering belt back on, the noise comes back. If I then remove the AC belt, the noise goes away. And so on.

Here is a video with clearer audio: https://www.youtube.com/watch?v=1wF51unJnUo&feature=youtu.be

Originally Posted by fastone53w

I had thumping/knock while in gear and stopped or just truck moving slow at idle.

Took me 2 weeks to find it and it got louder as time went on. Sounded like engine compartment from inside truck.

The flange on rear tail pipe flange just after muffler rusted off. The knock was the exhaust system moving around and as the flange started to fail more and getting loose and more movement and louder thumping/knock until it came apart and it stopped, but then I could hear the separated pipe rattling on cross member. That's how I found it. Put new muffler and tail pipe on and no thumping/knock sound.