V8 noise during cooldown

["Fabry, David" <fabry.david@mayo.edu>]

I have been lurking in this newsgroup for the past month, but now I have a
question for the collective wisdom of those who post here. We recently bought
a 93 V8Q (approximately 43K miles), and now that the temperature has risen
above freezing in Minnesota, I have noticed a strange sound emitting from the
car during cooldown after it has been driven for twenty miles or so. It is not
the usual exhaust noise, though I haven't ruled out exhaust/catyltic convertor
sounds as the culprit.  Basically, when the car is shut off, there is a
resonance that almost sounds like a sticking brake drum; of course, the car is
not moving when this occurs.  Initially, it occurs about every thirty seconds,
for a duration of five seconds. This decreases in frequency until it stops
completely after about fifteen-twenty minutes.  Any opinions would be
appreciated.  

Thanks,

Dave Fabry