I had a brand new serpentine belt i put on with a brand new alternator about a year ago and have barely drove the car so i know its not the belt itself. last night it was the coldest night we've had i'm pretty sure and when i turned the car on, i heard a terrible scratching/squealing noise. opened the hood and saw part of the belt came loose and part of it was off. what could of caused this to randomly happen? it's also not the air compressor locking up because i disconnected it and it still has the same problem. i dont think its any of the pulley's too because there was no bad sound warning me before it came off. this is just random. what could it be?