Rear vibe noise at 2000 RPM - 1st & 2nd accellerating

Hello All - Hopefully someone may have an idea on this, it has me stumped!
I have a 1999 323i which has a quiet (but getting louder) vibration noise coming from the right rear when the tach passes 2000 in 1st and
2nd. It only does this in gear. I only notice it when the passenger windows are down, it's that quiet.
The sound is like someone running a stick over a washboard, like in a hillbilly band.
Any ideas?
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I Ride Roads wrote:

Driveline imbalance?
--
-Fred W

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