Every time I turn on my rear defroster it makes an annoying noise. Even when the mode is on the foot well and front defroster. Not really sure if warming up or something with my heater is the problem. I do wait at least 2 minutes to warm up before I head out.


If you mean the rear defrosting wires in your rear window, you should be able to turn it on immediately as it's electrically based. If it's making a noise, I suspect it's the circuit breaker that automatically turns it off based on heat, and you should look into replacing it. What make/model is it?

If, alternatively, you have some sort of auxiliary/rear blower, the noise could be the auxiliary/rear blower motor as the bearings are prone to failure.


From the comments, it sounds like this is not a motor issue and varies with engine RPM, which indicates to me that you have a loose belt or worn belt tensioner (causing the loose belt) to the alternator, or an alternator with a bad bearing.

  • It's an '04 Nissan Sentra. The noise will go off on start up and when the rpm is around 2000 when accelerating. It doesn't have rear blower.
    – Jake
    Jan 15 '15 at 0:33
  • Is it coming from the engine bay? It sounds like this is your alternator/serpentine belt slipping due to the additional draw from the rear defroster, could you check the tension on your belt?
    – Ehryk
    Jan 15 '15 at 0:45
  • Yes it's coming from the engine bay. I believe it's coming from my alternator. The belt seemed to be fine. Not really sure what to replace.
    – Jake
    Jan 17 '15 at 17:42
  • Even if the belt may be fine (difficult to tell, typically you take it off and invert it and look for cracks, or just replace it anyway), there may not be enough tension on it, which causes noise as it slips. I'd first check the tension, then replace the belt, then replace the alternator.
    – Ehryk
    Feb 10 '15 at 4:53

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