Vibrating Noise While Heat Is On? on 2001 Mazda Protege

The fan belt was tightened and the oil was changed. On the way home from picking my car up, this obnoxious vibrating sound started when I turned the heat on. When I turned it off, it stopped. It sounds like its coming from the passenger side. My car did not do this before I dropped if off for these two things. Help... It's driving me NUTS

Asked by for the 2001 Mazda Protege
The most likely source of your concern is the heater fan blower out of balance. This is commonly due to something foreign dropping into the "squirrel cage" fan blades such a parking stubs, pencils or an occasional french fry. We have seen blowers fail on there own without anything in them though. Most likely the entire blower motor will have to be repalced unfortunely.