[77newell]

Brad: wow, you have a unique issue. On my 77 coach I had a sound that may, and I emphasize MAY, be related. My front air tank had a valve on the top that allowed it to be refilled from the supply tank in the rear but not allow air to flow the other way, a check valve of sorts but it didn't look like the typical check valve. The sound was a "eeeeEET" rising in pitch with a sharp cutoff as indicated by the "T". It would repeat this sound as the tank repressurized. I didn't have a 120v pump so the tank would completely deplete when camping. One way to tell if this is perhaps your case would be to shut off any air pressure supply and see if the sound eventually stops and if the brake pressure indicator drops.