Electric fan makes sound on 2001 BMW 740iL

Thanks for the answer, but my electric fan in front of the radiator also sounds abnormally (more like a helicopter) when comes on. I checked the fan and it does not seem to have any problems on sight. The sound is very annoying. I also saw the same thing on a couple of old cars (4-8 yrs old. one was nissan altima). What might be the problem?

Asked by for the 2001 BMW 740iL
Sounds like your fan is running on the highest speed, or the fan motor is going bad. It may be that this is normal too though. Can you stop by the dealer and ask them, they will have seen many of these and may be able to tell if there is a problem or not?