If its already at operating temps, I wouldnt run it for more than a minute. Thats plenty of time to find whats loose. In fact, only run it long enough to see if the noise stops. If it does, shut the engine down and test each pulley. They should spin freely and should not have any lateral movement (shouldnt wiggle) They wont spin like a bicycle wheel or anything like that but the should spin easily without seizing up at all during a full rotation.