I have a 2000 Saab Conv SE Turbo with 72K miles on it.  It has a 5spd
tranny. I am not the original owner, but I have complete maintenance
history on the vehicle.
Anyway, the car seems to drive very well, good power, smooth
acceleration.  The problem is I hear a very loud noise from engine.  It
can be heard from outside the car, inside the car with or without the
windows down.
It sounds like someone is brewing a big pot of coffee under the hood
(or like a kid blowing bubbles into a cup of mike).  I checked the
engine and it seems to be coming from turbo charger area, but I can't
be certain.  
Any ideas?