Here is my predicament which may be what you're describing. I hear a rhythmic pinging noise when the engine is running and for a while after it's turned off. It's not a high ping. Maybe it does it every 20 seconds or so. It seems to be coming from the rear passenger side. I brought the car to my local fix-it shop and the guy listened and thought it was in the door and probably coming out the speaker. (He said his stereo system had been hit by lightning and even when it was off, it would crackle occasionally.) When I leaned over to listen to the speaker, the noise stopped. So that means I can't take it to the Acura dealer right now (40 miles away). I've heard this noise before, and then it's disappeared.

Any thoughts?