What does it mean when a microwave makes a whistling noise every time it is being used?

Could be a leak in the seal of the door. I think I’d call a microwave store or department and ask what to do about it, if that is what it is.

Microwaves have a fan that turns on when the magnetron (heating piece) of the microwave is energized. My guess is that one of the vents on the back of the micro is partially blocked and the whistling noise is the air trying to squeeze out. Look around the back and bottom and see if the vents are being obstructed.

@elbanditoroso I like your answer better than mine. It’s more likely to be correct, too.

Furthering @elbanditoroso‘s answer it could also just be a fan that needs lubrication. Not sure the kind of whistling though.

Thanks. I do keep a lot of stuff in that area so I’ll check around it.

I’m not sure how to describe the whistle other than it is very loud, screeching and extremely annoying. I close the door and can still hear it in the other room.

@carrielynn Could be the transformer going bad, I think it might be time for a new microwave.

When my microwave went bad, it produced a loud low hum.