Slight vibration around 1600-2000 rpm

[oceancab]

The vibration goes away once you get out of that range, I'm inclined to think it's either the engine or transmission because this happens no matter which gear I'm in.

[JodyStevens]

Is the vibration felt through the steering wheel or through your seat?

Its probably a good time to change your engine mounts, trans mounts, guibo and CSB.

[KenB]

Guibo? Center bearing?

[Mike W.]

What's your exhaust system like? Could you be feeling a resonance in the exhaust system? Engine and exhaust are the only things that are RPM sensitive, tranny thru diff are speed sensitive.

[oceancab]

I was mistaken, it's only noticeable in 3rd gear. The vibration is all around, I can feel it through the steering wheel too, but really the whole chassis has a slight shake to it.

The previous owner took the exhaust system from a 6 series.

The vibration started after I did a donut in a parking lot >_<

[GripGreg]

Like Ken & Jody suggested, check your guibo with a flashlight.
You're looking for signs of tears in the rubber.

[oceancab]

I took a look at the guibo and it looks new. Is there a way to check the center bearings without having to remove the driveshaft?

[Eric Q]

My experience with center bearings is when they wear there is a vibration (or a knocking against the driveshaft tunnel with severe wear) upon takeoff from a stop. That is when the most torque is applied on the shaft, causing it to bend slightly. The vibration goes away after a second or two when the driveshaft straightens out.

[oceancab]

Actually, the vibration happens at 25-30 mph no matter which gear I'm in.

[Falkenberg]

Depending on the frequency of the vibration, it might even be a tire / wheel problem.

Maybe it's worth to check your engine and gearbox mounts - on my E32 the gearbox moved out of line once after making an enthusiast left turn. Besides a short moment of scary noises I also got a vibration.