If you are referring to the blower motor squealing, then I would suspect the blower motor bearings have failed.
Change the belt
The squeal when you turn on the AC or heater is a loose fan belt. It may be cracked and need replaced, or it may just need tightened.
In my experience this would be because the alternator belt needs to be tightned.
The window regulator ( the part that moves it up and down) has failed and will need replaced.
Usually when a car makes squealing sound after accelerating with the heater on, the serpentine belt is a little loose. It likely needs adjusting by a professional.
A squealing heater is more than likely a fan belt. It may be loose, or it may be worn and need replaced.
Loose belt -- replace or lubricate ADD-ON If it is a metallic squeal that continues for a minute or so after the car starts it could be your water pump bearing. Get your mechanic to check it out and replace before you need a tow truck.
Its happening to me too i'm almost convinced its a loose serpentine belt
That's usually an indication that the fan motor bearing is worn and/or dry.
Automatic transmission fluid does not squeal. You have a different problem. Brakes squeal, bearings squeal, and belts squeal. Fluids do not squeal. You had better take your vehicle to a mechanic.
squeal of fortune
Here's a sentence with squeal as a verb: "The child will squeal when he opens his Christmas present." Here's a sentence with squeal as a noun: "The child's squeal was deafening as he opened his Christmas present." Let me hear you squeal like a pig.