I just bought a 2002 ford f-150 lariet crew cab truck. Every time I turn on the headlights I hear what seems to be some kind of fan running behind the dash board. Even if the ign. is off. What is this? It loud enough to bug me when I'm driving.

 

A fan, or crackling noise like dirty switch contacts arcing ?

 

thanks for the quick reply.
it definetly sounds like a motor or some kind of cooling fan running. seems to come from behind the radio/ dash area. key is off & no other accessories are on. very strange!
any ideas on what it could be?
thanks!
jim