I am becoming highly annoyed by a noise in my '02 with 118k miles, and even more annoyed that mechanics can't figure out the problem. It consists of a tinny metallic clanking or ringing, similar to an exhaust heat shield rattling. It seems to be coming from somewhere behind the engine and could be as far back as the rear of the transmission. It is most noticeable on the highway, only when I have the lightest touch on the throttle, but not enough throttle to keep the car at a constant speed, the car will be slowing slightly. When parked I can barely hear the noise (I think) if I rev the engine; it'll faintly occur very very briefly as the revs come back down to idle, and I can only hear it if I'm bending down outside the car with the door open as I rev it.

I just had the car up in the air and inspected. I had the heat shields removed from the front exhaust pipe and the pipe appears fine. All maintenance is up to date, and trans fluid is fresh. Anyone have any suggestions on what it could be?