[CaptainGizmo]

That’s pretty funny because I’ve always had that buzzing and this last week we were tracking some of that down. It’s pretty easy to figure out which is anytime the main air is higher than the brake tanks. I think what’s happening is it’s transferring air through that check valve, which tends to buzz. And, since air brakes constantly leak, that air purges by the check valve causing to buzz.

This evenIt will happen right after I’m running the engine and then dissipate after a while. HOWEVER, now that I’ve got my coach set up with shop air, that supply actually is set up to charge ALL the tanks, not just the AUX tank. I presume the principle is to save extra wear on the on-board compressor from constantly filling the leaky brake tanks. So, that is obviously held back with that check valve.