Originally Posted by ChrisAW
I had a cowbell noise that would happen whenever i would put load on the drivetrain or whenever i would come off the throttle and there would be negative load on the drivetrain. Loud cowbell/ping noise. It turned out to be the driveshaft and the dealer replaced it under warranty.
Yet another alternative source to the sound. Interesting. Diagnosis of this problem could be harder with so many different possible causes. The same can be said for recreation of the problem for service techs. Luckily when I took mine in the second time, it was continuous, and the tech knew right away what was up (in my case, pebble INSIDE RR rotor - not between rotor and heat shield).