Q: My car is making a weird high-pitched whirring sound - 2000 Pontiac Sunfire

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Over the past few months, I have noticed that my car starts making the high-pitched whirring sound whenever I have the heat/AC on at 55 mph. More recently, it started making the noise, even when I had the heat/AC turned off.

Tonight, I started my car, and it started screaming - it was the same whirring noise, only a lot louder. I restarted it, but the noise was still there. So I figured I would turn the heat on, and then, the noise stopped. I didn't drive past 55mph afterwards.

When I got my car a year ago, the dealer informed me that the part(s) that controlled the heat and AC were in the trunk upon receiving the car. We split the cost with them and had it fixed. It worked fine after that.

About 6-8 months ago, the heat/AC started working only on the highest setting.

My battery has been checked and is working fine.

Could the sound have something to do with the AC/heat? Or could it be something to do with the alternator?

My car has 109550 miles.
My car has an automatic transmission.

Hi there. In most cases when you hear a screaming or squealing noise under the hood, it’s related to a belt that is loose or is beginning to show signs of wear. Since you’re having AC issues, the problem could be related to the serpentine belt, as this belt operates the AC pump. However, the noise could be coming from the blower motor as well.

The best way to diagnose this problem is to have a professional mechanic, such as one from YourMechanic, come to your location to complete an inspection to determine why the car is making this noise.

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