Randy, the auxiliary pump under the stairwell is meant to work when you are using the Auto Level mode. Once leveled initially using tank air, the Auto system checks in every 30 mins. or so to see if you are still level. If not, one (or both) of two things should happen - it will let air out of a high front (which has only one, centrally-located valve) or one of the two rear valves if a rear side is high, or it will activate the little pump to inflate and lift the front or a rear corner bag(s) up.
Be aware of course that if the site is relatively uneven, the system may not be capable of Auto-leveling, and may require repeated attempts starting from a very low position by dumping air first. Other times it may let out or add air to particular bags right from the Travel Mode get-go and find level just fine. Manual leveling is occasionally the best option, but the auxiliary compressor in theory shouldn't kick in if you go that route since in that case there is no automatic 30 min. balance check performed. The air bursts you hear are likely the auto-level sensor triggering slight adjustments to a high set of bags, and air releasing from one of the three valves - front, or left or right rear.
It's not uncommon to have the balance sensor in the HWH module go awry and need adjustment. Check this by air-leveling the coach using the lights on the HWH panel, and then placing a leveling bubble device on the fridge floor or on several test spots on the central tile floor. I don't like countertops for this since they can vary from true level from counter to counter. I like to use a little inexpensive square level with a central bubble that reads all directions at once. But I've also just used a golf ball on the kitchen floor to see if it rolls one way or another. If the panel says you're level and so does the ball or bubble, no adjustment to the sensor is required. Otherwise HWH's website should have instructions for that, or I have them somewhere in my stuff, and pix of the adjustor - as I recall you get balanced as per a ball or bubble level, then tweak the adjustors until the panel lights all go out.
Some here may add to or correct my expose above, but that's how I've come to understand it.
Joel