asterisk users - Mar 2005 - Short burst of static then disconnect

I've got a box running CVS-HEAD-02/18/05-02:27:22 with a digium single 
span T100P card.  With increasing regularity we get inbound calls that 
will work fine for an arbitrary ammount of time (some calls last over 
20min before the problem) then they are interupted by a short burst of 
static and then the line drops.  On the console I see:

   == Spawn extension (did, 7214, 2) exited non-zero on 'Zap/24-1'
     -- Hungup 'Zap/24-1'

which is the normal behavior for a correctly terminated call.  Any ideas?

All the phones are Polycom soundpoint ip500's some are local some are not.

Thanks,
-Ryan