I bought the car form the auction and have so far replaced the water pump, brakes and the belt, but there is a loud screeching grinding noise cominf frim under the hood, what could it be. I had someone look at it and they said that it it is the compressor but I am not sure I believe that, do compressors make a noise like that when they go out. Just trying to avoid getting ripped off for repairs that I don't need. Single mom in school. HELP PLEASE.