Originally Posted by gloran
Dan when I bought the coach in 2002 I read through the Owner Manual cover to cover. It mentioned the air tank and the need to drain moisture out of it routinely.There was a drawing showing where it should be located under the coach, wasn't there. Then as I started investigating other systems I found numerous things changed and not where the manual said should be, and the manuel stated there could be changes.I've tried to follow the 1/4" air line and have been able to follow most of it from the compressor down to the drivers side frame back to the rear air bags,and with the painting time spent under it I haven't run accross any tank.
There is a small plastic tank about the size you discribed above my compressor. This tank has no draining valve, I have air horns and from the compressor a yellow airline goes to this tank and then on to the air horn. the red air line goes to the air bags. I always figured this tank was just for the air horns, maybe this is the tank?
It was kind of hard to see what was actually happening in the picture but if that tank is connected to the compressor that also supplies the air bags then that is the tank. I see a solenoid valve there which could be the noise you mentioned. Like I said before the check valve protects the compressor from hard starting against high tank pressure. It also prevents tank pressure from bleeding off back through the compressor valves. When I bought my new Viair compressor it came with a check valve with the warning that removing the check valve would void the warranty. It is not an Airstream only kind of thing.
Now back to you original problem, I would look at your leveling valve or valves. If you squirt them with soapy water and don't see any bubbles, also squirt all the fittings, put the exhaust tube from the valve in a jar of water and watch it for awhile for bubbles. If the valve is leaking internally it will exhaust air through that tube. This is assuming there are no leaks around the compressor and plumbing up front. Be aware that a solenoid or check valve up front may also be leaking so you may need to tap into a fitting somewhere to install a gauge to monitor the pressure at the tank.