Sounds like the fan is singing its death song.  Eventually this will cause
the fan to draw more current and blow the fuse.  On my '85 Vanagon this
caused the wiper blades, fan blower and a few more things to stop working
(which was kinda inconvenitent 'cause it was raining).  I can get you a good
used blower motor for $25 + shipping.
Ken Wilford
Van-Again
John 3:16