Squeaking noise when heat is on
 

My 2014 with 70,000 miles has just started squeaking when the heat is on. It is most noticeable by the passenger's upper vent. Not real loud, but consistent. It is not apparent in the engine compartment.

Any idea what it is, or what I should do about it?

So no noise with A/C on or off? Only when on hot air?

Does it vary in speed or loudness with a change in fan speed? Does vehicle speed affect it?

I turned the thermostat down as low as it would go and couldn't get the heat to turn off without also turning the fan off; it is pretty cold out. Turning the fan up drowns it out, so I am not sure what effect it might have. Having the A/C on also didn't affect it. No, it doesn't change with engine speed.

However, the last couple days it stopped squeaking. Not sure if that is good or bad news.

Squeezing noise when heat is on
 

So my Mazda is also having this constant squeaking noise with heat being on. It’s driving me nuts and I want to get it to stop. Any ideas would be helpful so I can fix my car. Very annoying. The nose doesn’t change with speed of car, nor with turning the fan or heat up or down, the fan does indeed drown out some of the noise, but then I also can’t hear my music. I also cannot continue to have the fan up all the time and prefer to have my Mazda set on auto (minus the A/C) at 70*. I was hoping to find the answer to my problem with he previous person but it never got answered as her issue stopped on its own. I’m the o my owner of my Mazda since day one and it is a 2017 Mazda 6 coming up on 3 years old from when I bought it. I drive for a living so my miles are up there. Please help!

go behind glove box to locate cabin air filter. carefully remove filter as leaves and debris can accumulate on top of filter. due to the design removing cabin filter can cause debris to fall into heater fan housing. you may be able to reach inside to feel if anything there. If anything in fan housing you may experience a noise when fan turned on. Had dealer service my car, they checked cabin filter. when i got in car noticed noise from fan and they found leaves in housing, Since first service after purchase, I suspect its from when they removed it.