I have a 90 740 gle wagon w/ 152k miles on it. there is a tinny buzz at approx 2400 rpm. I have traced it to the exhaust system where it comes off the manifold. It appears to be a 2 layer pipe of some sort. Any suggestions on how to stop it from buzzing. (and please, no comedians telling me to keep it under 2400 rpm).

Also, the radiator flange just failed, which I understand is a common failure (it is also common on BMWs which I have much more experience with). I used some abs/pvc glue to glue a piece of pvc pipe inside of what was left of the flange and glued a second piece of pvc around the first piece to bring it up to the proper outside diameter so the hose would fit properly. I reinstalled the hose all the way up on what was left of the original flange and tightened the clamp. Has anyone else tried this repair, and if so, did it hold up and did it restrict the flow of coolant too much? I just did this, and so far it seems to be ok.