I noted this on my '91.

     A helpful list member suggested adjusting the thermostat knob slightly
     to perhaps stop this (indirectly).

     Before I got a chance to try this, my fan literally burned up and came
     close to setting the interior of the van on fire (I posted on this in
     July).

     I now have two of the Radio Shack muffin fans on the fins (and sheet
     aluminum behind and under the fridge in case something else decides to
     emit flames sometime in the future) - they're way bunches quieter and
     don't wake me up at night.

     In retrospect, I'd have to suggest that the problem may actually lie
     with the thermo switch.  Mine's a bit loose and I can imagine that the
     slight vibration of the stock fan coming on may be enough to affect
     either the internal latching of the thermostat or the thermal
     connection to the fins.

     -Blaine