2000 Chevy, 2500, 5.7 It sounds like a broken belt coming from the dash. It does not stay in time with engine rpm's. It comes and goes at any speed from idle to highway speeds. It does not make any difference if the HVAC system is on or off. Just replaced the air blend actuator and found heater core has been leaking which will be replaced next week. Does it make sense to anyone that the leak could somehow be connected to this noise? Chime in please, and thanks.