Whenever I turn my AC or Heat on in my car, I hear a loud squealing or grinding noise...

Hello
Firstly, what kind of noise?
1) it could be some thing got into the fan blades and with the fan running = it makes noise.
2) Maybe you got worn out bearings on the fan blades

What is causing that irritating noise? ' DSMtuners

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Is it squeaking noise, Loud rubbing noise? Brake problems? Clanging noise is bad engine problem. Was oil that low that they needed to add it. Have you checked it again since that? Do so immediately, If low, take it back NOW.

could be the heater fan, could be the a/c clutch, could be the a/c belt.

Your AC compressor on the engine is the likely problem, either the pump is frozen up or the front bearing is frozen up, don't run the system or the belt will burn and fly off and strands you. Get this taken care of right away before winter. Have a local shop listen to the noise to confirm my guess as to the cause.

SOUND LIKE AC COMPRESSOR PULLEY BEARING SEIZING UP.

What kind of noise? If it's like a squeal it is a lose belt. If it's more like a clunk it's the transmission shifting and you just happen to notice it more because of the higher RPM the motor is at with the AC on. Try getting the vehicle moving with out the AC on then turning it on after you are moving to see if you get the same sound. If it's a squeal you have a loose belt that needs replacement or tightening.

it is the a/c bearing clutch. it needs to be replaced

Does it happen every time you turn on the air

If the noise going away every time u turning off the ac it's probably your ac compressor belt.however i will suggest to take some vaseline and rub it all over the exposed parts of your drive belt.