man o man. so car is running fine all day. after work i get in, and start it up and i hear a god awful high pitch sound that gets louder with rpms. sounds like metal clanging around.....but the car ran fine. by the time i got home, the sound had gotten MINIMALLY better, but still very audible. what could this be?? it idled fine and drove fine. BTW, its like -5 degrees out here. but it has been for weeks. never did anything like this. any ideas? yes i checked the oil.