Droan noise in exhaust manifold area--86 951?

[Vroom]

10/17/01 Noise continues from engine exhaust area. Has anyone been through this?

The noise comes on after the car warms up and while driving. A droan between 1900 and 3000 rpm, in gear or in neutral. Rennwerke in Elmsford, NY, agrees with my tech, it’s not hurting the car. The parts guy at the local dealer said there was a service bulletin regarding exhaust manifold double walled pipes, on 944 Turbos, breaking up, and that the new replacement parts would solve that problem, but that it was an expensive job.
Have any of you had the same problem? It drives me crazy. When I get off the highway, I can still make the noise by idling in the 1900 and up range. But a minute later, it’s gone.
If I can determine which part is the culprit, then the mechanic can change it. He just doesn’t want to waste my money looking for it. I’m hoping that it’s a problem some of you have also had, and that you can lead me to the culprit??
Thanks,
Ave 1986 944 Turbo 140K


9/8/01 Update: mechanic’s opinion about drone noise coming from turbo area

Hi guys, My mechanic has spent a fair amount of time trying to isolate this noise. We can get the noise on the highway, but not in the shop. He pulled the boot and checked the turbo, says it is fine. His feeling now is instead of spending hours and big money looking for it, he’d rather I drive it a while and hope the noise gets worse so he can find it in the garage, says it’s probably one of the exhaust pipes coming from the turbo...says these pipes are double walled and the inside wall often deteriorates, but says there are several pipes to consider and he doesn’t want to go searching without being sure of where to go.
He disconnected the turbo and tested, and discovered that the car ran without the noise, so it IS related to the turbo, but not the turbo itself. Anyway, we’re getting closer.
Have any of you experienced this kind of drone noise coming from the engine when you are accelerating in 4th and 5th, or even de celerating. The times when the air movement is the strongest in those pipes I imagine?

Any advice? He says I won’t hurt the car by driving it. But he doesn’t want to waste my $.
That I’ll just have to live with the annoyance until it develops more clearly.

I left some of my previous notes about this below.

Ave new owner of 86 951