Help: 164 noise?

[ross6200 <maxchiming@xxxxxxxxx>]

Can anyone diagnose this:

A loud humming noise coming from just behind the firewall, in front of
the passenger seat.  At least I think that's where it's coming from. 
It only happens when the car is in gear...almost always in lower gears,
and sometimes in 4th and 5th. Sometimes, it goes away completely in 5th
gear.

It doesn't sound like a loose belt (like you'd hear with heavy
moisture)...
anyone have any ideas?

Thanks (even my mechanic doesn't know).

Ross (1991 164L)  
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