loud screeching noise

If by heater you mean the defrost then it sounds like a/c compressor kicking on and stressing the loose or worn out belt. Make sure to check belt and any pulleys/tensioners related to that belt. Could also be related to fan motor when turn these systems on.

Sounds like you might have a loose belt or one of the pulleys are going bad. The reason you only hear it when you turn on the a/c or heater and accelerate is because you are putting it under a load.