when my car is in motion I hear a noise coming from the motor and it sounds like a belt is about to snap but it only sounds when i'm driving and it doesn't sound all the time.. but when it does i sometimes hear it all the time unless i come to a stop or sometimes when i'm driving i hear it and then it stops for a few seconds to the whole car ride then starts up again? and everytime i bring it to the shop it doesn't make that sound. Does anybody know what could be making this sound?