strange noise from under the glove compartment

The day after I replaced my battery a strange low frequency whirrling sound started. it seems to be coming from under my glove compartment. The heater blower perhaps? it makes the sound on both the turning on of heat and or the air conditioner. it just started yesterday. my car generates heat just fine. Does this mean the motor/fan is going out and is it an expensive fix? or will my heat continue to work just fine for a long time but i will just have to put up with the annoying noise. Since i amc not get off work till next February and can not afford repairs. should i invest in one of those portable car heaters just in case? should i worry about staying warm in my car this winter?