Help: strange noise

[Mike <mac50@columbia.edu>]

Hi again.  This list is great!  I have lots of questions.  This one 
really worries me.

My 89 Audi 100 is making a strange noise when in "drive".  It makes a 
"click click click" sound like a playing card stuck in a bicycle wheel.  
The sound increases in frequency if I accelerate, stops completely if I 
shift to neutral or park, and sometimes goes away if I really step on the 
accelerator.  Since it doesn't happen in park or neutral, listening with 
the hood open is fruitless.  Besides it seems to be comeing from outside 
the engine compartment.  Its best heard when driving through an enclosed 
space, like a tunnel.  BTW, car had 47K miles on the odo.

I noticed in the archive another similar problem described; is this 
problem common to Audis?  More importantly, how much will it cost to fix?!

Thanks in advance,

Mike

89 100