How are you reproducing the sound...when it's not moving? So, is it reproduced by reving the engine in neutral or park, or are you turning the steering wheel, or rocking the body of the vehicle, or what? I thought you mentioned replacing motor mounts or was that someone else? If not, check those and the trans mounts. And we really haven't investigated the rear shaft much, is the front u-joint on the rear shaft okay? Since you've had a major repair done recently, slide around underneath just looking for anything odd, maybe something has come loose or was forgotten, during or since installation?

Another known area of wear is the watts linkage attached to the rear end. It usually knocks when bushings are worn. You usually can reproduce the noise by rocking the body from side to side.

Had the heat shield over the muffler come loose and produce a rattle once...but not really a knocking noise.

​​​​​​​Also, wasn't able to listen to your cloud video.

Brian.

 

I am able to reproduce when not moving as follows:

With the front wheels up against a curb and the truck in drive, I push the accelerator pedal so the engine revs up under load. The wheels are not spinning, and the truck is not yet moving and I still hear the noise. I dont think I can reproduce in neutral, as I have to give it about 50% throttle to do it. It kinda seems triggered by weight transfer or perhaps engine rotation. I read somewhere that it might be something loose and when the engine rotates a little on the mounts it could touch something.

The motor mounts are brand new. What should I look for on the tranny mounts besides obvious failure?

I have spent much time underneath banging on stuff with a rubber mallet trying to find something loose but I can't. Also looking carefully in the engine compartment for any signs of things out of place. I will go rock it side to side now and see.

I really don't want this to be an engine problem, and I don't think it Is since I have no codes and power seems real strong.

Thanks as always.

Lets summarize:

• Sounds like 3 or 4 distinct "knocks" or "clunks" like someone rapidly knocking on a door (but not really loud like a knock, much more subtle)
• Happens under acceleration or revving up under load while stationary.
• Sounds like coming from engine compartment on the drivers side or down by the drivers' pedals.
• Almost sounds like it is coming from behind the dash.
• Can not really hear it if you are outside the car squatting by the suspension (seems like not CV, wheel bearing, axle?)
• Happens independent of wheel speed, engine speed (probably, it could be happening at the exact same RPMs and sounding the same each time).
• Probably not driveshaft: occurring with two separate drive shafts.
• Front diff and transfer case are full with new fluid.
• Easily triggered when accelerating under 1/2 throttle when traveling 30 MPH
• High speeds: no vibrations
• Can avoid by babying throttle.

 

Okay, although the motor mounts are new...l'd be checking them over very closely for looseness (not installed correctly, missing bolts/nuts). Have someone simulate the same conditions as you, but this time (against curb)...you stand along side the engine compartment, hood open, and watch the engine for any unusual/excessive movement. You can check the trans mounts by lifting trans with a long prybar...and looking for movement in mount.

Brian.