The car is a '92 325i, and I recently noticed a very high pitched, very nerve wracking squeal coming from the ventilation fan (for my lack of a better term). The sound goes away when either A) I turn it off, obviously, or B) when I turn it to maximum speed, which I believe is "4" on the dial. Anywhere in between, the noise will occur. BTW, it does not matter where the air is coming out (dashboard vent, floor vent, defrost vent). Any thoughts on how to remedy this? My ears thank you very much.

had simalr problem on my 318 race car opened fan housing and used contact cleaner on brush assy and lubed bearings has been noise free since