quattro - drive vibration ?

[Solomon Ngan <sngan@netaccess.on.ca>]

Hi,
I have this vibration for a while which I have blamed the tires for it. 
But with new tires the vibration is still there.
What I have identified is that the vibration seems to come on when I
have my foot on the gas pedal.  When I let go, the vibration is gone. 
Does it mean there is a problem with the AWD , its bearing, or something
related to it ?  Or, is it normal for 2nd generation quattro system -
'90 90q20v ?
Any experience with that ?

Solomon Ngan