My 1989 560 SEL has a very irritating buzz coming from under the right side dash. I took the underside panel off, exposing the small part that is making the constant noise. It is wrapped in about 1/4 inch of insulation. It includes a silver box about the size of a pack of cigarettes. A small fan (maybe an inch in diameter) is coming out of its side and blowing into either a hose or cable that then leads up the wall and into the bowels of the upper dash.

This buzzing part sits about 9 inches above the Engine Control Module. In fact, until I really pinpointed it I suspected the ECM was buzzing.

There is an electrical plug that enters the box on the opposite side from the fan. It apparently can be unplugged, but until I know what it does I will not do that. I will just continue to turn the CD player up higher until I can fix it.

The buzz starts when I turn the key on accessories and continues once I start the car.

I have a shop manual on CD but I have not found this part. I have looked on all sorts of parts catalogues and have not seen this part.

Please help me ID this mystery part and tell me is it essential. If not, I will remove it until I can buy and install a replacement. Otherwise, I will drive in ignorance.