As soon as I turn off the heat, the whistling sound dissapears
it is probably the bearing in the fan motor or some debris that has worked it's way in there. worry about it when the noise is constant. it
Yes the motor could be locking up, it could also be some debris in the motor fan. Leaves or pine needles, etc. FOURFROMMOORE
Sounds more like a heat or fresh air door is not closing all the way. My pathfinder does that from time to time.
Quite likely it is,- when bearings get dry they squeak or chirp the more worn the louder the noise and more frequent! I may progress to a point where it goes into a low growl At this point it is past worn out,- and will blow a fuse if let run very long (as it draws excessive current this way)! Are you talking about the blower motor-- (as turning off heat), -- or just changing the blower doors to another position, -- (blower still running)-like going from floor heat to defrost? If this is the case, then you might have a piece of paper or a leaf, - or a label off something trapped in a place where it vibrates like a reed in a musical instrument-- this would likely change with blower speed!
If the motor is running (blower) and is quiet, it is not blower related. There could be a vacuum leak from a worn out switch.
