[RussWhite]

I have a possible explanation. At the small air tank located near the drive wheels on the passenger side ( if you have one there ) is a check valve. This valve's purpose is to retain pressure in that tank even when the main aux air goes low. Usually this tank serves the toilets and doors. I have found that the valve will whistle and sound like an air leak when air to entering that tank. So, if you are using air from that tank and air is entering from the main auxiliary air source, then you may hear the check valve and think it's a leak.