Belts squeeling

[bgsterling at bluebottle.com (Brad Sterling)]

<snip Julie> 

Yet again, the belt from the WP to the compressor is loose. Its only 2 weeks
since I tightened it.
Could the compressor be slipping? 

<end snip>

When I had this problem, I was missing one of the bolts on the WP.  There
was enough friction to hold the pump in place, but after some driving, it
would slip and the belt would loosen.  After retightening a couple times, I
finally took a *good* look at the pump with a flashlight and noticed the
missing bolt.  

-Brad
'86 Scirocco 16v