My son's 1994 Grand Am (3100 V6) is making a sporadic high-speed rattling noise, originating from the back of the engine compartment, driver side, better heard from inside the car. The frequency of the rattle is constant -- it doesn't change with accelerating or decelerating, so it's not coming from any fast-moving engine parts. It's there for a few seconds and then it goes away. It cannot be reproduced on demand. I've heard it twice -- both times after the car has been driven and is still warm. Does this ring a bell for anyone here? Thanks. Svilen