loud buzz goes away if I lift up on steering wheel

[treed2 at wsu.edu (T. Reed)]

Lately I've noticed that at certain RPMs, particularly (but not only) 
idle, the steering column seems to start vibrating against something and 
makes a loud buzz that can be heard over the noise from the engine, blower 
fan, and cd player combined. The only way to make it stop is to change RPM 
or lift up (or sometimes, push down) on the steering wheel.

What could this be? Loose steering column bolts? Bearings disintegrating?

I know the standard answer is the passenger side motor mount (it -has- 
been about 30,000 miles, but I don't have access to a press anymore) but 
I'm fairly sure this buzz could be fixed by itself without fixing the 
underlying cause..

Ideas?

-Toby