Recently developed a problem with A/C / Heater fans. When I start the car, the fans run full with controls off then slow down to what sounds like a separate fan running. When I turn on A/C or Heater, I hear additional fans come on. Turn them off and they seem to stop but there is still a separate fam running. What I am wondering is whether it is possible that the parked car ventilation system has somehow been set to run all the time? Any suggestions would be appreciated.