My 1995 LS400 (2nd gen) with only 115000km (71k miles) is making a worrying "knocking" noise in accord with the engine revs.

I tried to record it (from the passenger side, with a phone), unfortunately you have to turn up your speaker volume to max to hear anything:
https://vocaroo.com/1ljoJftielmP

The knocking is audible slightly at idle (400rpm), most between idle and 1000-1200rpm (as in the recording), higher and the engine fan noise drowns it.

In P gear there is no knocking at all, at any revs.
In N gear there is also no knocking except 1-2 single knocks exactly when *starting* to rev the engine up, it's very subtle.
In R and all other gears it's permanent, at any revs, and the knocking frequency goes parallel with the engine revs.
I tested this while standing and with the E brake on.
While driving, it's audible in low revs (up to 1000-1200), then the engine/driving sound drowns it.

The gearbox fluid is at correct level (on the high side).

My thoughts:
It's not the the engine since there's no knocking in P gear.
It's not the torque converter either since there should be no difference of spinning parts inside the gearbox between P or any other gear *while standing*.

I got a hint that it could be a worn out parking pawl but since it is located at the output shaft which is not spinning while it knocks, I ruled that out.

I'm really puzzled with this. What's the difference between P gear and all the other gears (except N maybe) *while standing*? Is there anything more spinning, after the engine and before the wheels, when not in P?

 

It sounds like a shot transmission mount to me.

 

First guess would be transmission mount as well. Cheap & super easy to replace too, and a common part to fail with a ton of different symptoms.

If you're fully stopped, give it a good stab of gas to get going quickly. Does it feel like it takes a second for power to reach the wheels and like there is "slop" in the driveline? I would see and hear the engine rev, and then a million years later the power would make it's way to the wheels with a subtle thunk. That was my failure mode for my transmission mount. Replacing it made a huge difference.

Also, do you feel it through the shifter? That would be another point to transmission mount.

 

Thanks for the ideas, sounds promising. Will check the mount as soon as possible.

@400fanboy
The car is currently in a remote garage, so I cannot answer your questions properly.