Its a 2002 Z28 A4 with 110K miles.

Its not a grinding vibration....more of a harmonic vibration.
It occurs with the engine ON in all RPM ranges.....
Its a little more pronounced when the auto trans is engaged..parked.
Still there while driving.

Its not constant.....more intermittant....but consistent.
Like.....fine......then hummmmm.....fine.....then hummmmmm....etc with about 1 second inbetween.

The car still delivers about 300lbs of TQ in data logging with HP and gets around 26mpg on the freeway at 65mph....so I don't think its affecting efficiency.

Its just annoying......

I had the dealer check the motor and trans mounts and they say they are fine.......

I disconnected the belts and ran it ....still there
Throwing no codes.

What else could it be?
Could it be the harmonic balancer?.......it looks fine...meaning no wobble.

 

What happens when you are in Neutral?

 

Same vibration while engine is revving in neutral.....
It doesn't shake anything...like the rear view mirrror,
but I can feel it when its there an when its not there.

I guess it could be the mounts....just not visually apparent.
The engine lifts on the Driver's side about 1/4 inch when I rev it manually......how much should it move?

Could it be the torque converter?

Other than that....its a great car!

 

Just as an update......
It was the harmonic balancer/crank pulley.

Smooth as glass now......

I hate vibrations.

 

hey fasteddy, I think I have the same issue, I have this vibration, it comes and goes, it hummmms then it goes away then it humms. It will do it when the car is in drive while holding the car with the brakes, also do it under light throttle. Had my mechanic check the engine and trans mounts and he said they were fine. He also checked the exhaust and said it was all tight. So I might try this next, hopefully it fixes it.