I’ve owned this 1987 BMW since February, and after immense and expensive repairs, it became roadworthy. Recently there has been moderately high pitched hum coming from the Drivers side, approximately under the rear door area of the car. It seems to be coming from a part of the exhaust system(?). This part is white, vibrates, and is cylindrical in appearance.
The car only had one previous owner. He kept all record of the car over the year, so I know of no wrecks, repairs to the exhaust, and/or body work done to that area.
It is a menacing sound but doesn’t seem to be affecting anything, and it only happens occasionally. I have noticed it mostly when idling, but it still occurs some when in first and second gear.
Please help! Can someone identify this part? I’ve looked through a few diagrams, but I am unsure. I need to know the importance of this hum, and whether I should seek a mechanic.