I have a 2015 Toyota Camry when I turn on my heater doesn't matter if it's at low or higher RPMs it has a squill not high but it does squirrel a little bit just wanted to know what your thoughts were on that
Also, are you sure it's the belt? A bad bearing in the blower motor
could cause a squeal.
Belt wise you have the increased draw on the alternator from the fan
motor, and as Scott said, in defrost the compressor engages as well.
I would check the tensioner and the various pulleys and the belt itself
for wear. Do you hear any squeals when you rev the engine? How about if
you turn on the fan and rev the engine? What does the squeal do?
Just to add an experienced +1 to that comment above...
o I've had intermittent squeals that lasted for months that were bearings;
o I've had intermittent squeals that lasted for months that were belts.
I tried the stethescope diagnostic method, which many people suggest, but
an engine is so loud that, personally, I find that method worthless.
I also tried the spritzer of water on the belts method that many people
suggest, but, again, I found that method almost worthless in my tests.
I never was any good at pressing on the belt to test the tension (and I
don't trust those tension gauges any more than my finger), where tension
isn't everything anyway (although visual inspection is pretty good).
In the case of the bearing squeal, it finally manifested itself in the $5
alternator bearings having been the culprit, where the rebuilding took me a
weekend as breaking open an alternator isn't as easy as you might think.
In the case of the belts, the alternator belt eventually broke,
necessitating a parking-lot replacement of the broken belt.