I took my 997 C2S in for an oil change to the dealership a couple of weeks ago and from the minute I left, I got a loud buzzing noise from 3000-3200 RPM. I've taken the car back twice.

First time, they thought it was the mufflers. I replaced them (at my cost because they were after-market), but still have the buzzing.

Second time, they thought it was the oil pressure piston and they replaced it. Strike two...

I've tried to listen from the engine bay and from the bottom of the car and can't seem to figure it out.

It does sound weird that the buzzing could be related to an oil change, but I can't explain why it would go into the shop perfectly fine and come back with the buzzing.

It sounds almost like a metal or plastic piece is loose and is vibrating against something else.

It usually only happens in first gear -- every once in a while in second gear. It only happens when the car is warm -- oil temperature close to 200.

Any thoughts?

 

It could be related to the deck lid, it may need adjustment, something could be loose. Do you have an aftermarket wing?

 

i have that noise as well. I think it may be the cats, if they crack they can buzz.

 

Thanks Machina. I think you're right.

I hit the cats with my fist and the driver's side cat rattles a little when hit. I'm going to have the dealer check it out.