I have a 1988 560 SEC. The Air Slide Valve makes a humming noise loud enough to be heard over normal engine noise at RPMS over 2500. You can hear this inside the car at 65+mph. At idle you can hear the hum with a stethescope. The sound is very similar to that that comes from the alternator when it and the engine are cold. Kind of a throaty hum.
Is this normal ?? or do I have a developing problem with this valve and what happens if it does go bad. ?? Thanks for any help. LEE