With hydraulics my coach does this. One rear jack has very small leak and maybe once a day i will feel and hear a pretty loud bump. I'm just assuming it's the coach settling. Where I'm at now its pretty level so I just dumped the air and didn't put jacks down for about a week at first and no thumps. The bumps/thuds only show up when I decided to hydraulic level due to slight wind movement. So pretty sure it's the jack, but you could also have seals or valves leaking at the manifold at the pump.
What bums me out is that's a brand new jack as my previous jack got torqued with unstable base and wouldn't fully retract - it doesn't take much with this heavy coach. But last fall I was at a new park that had a lot of non compacted deep gravel and even though I had a good sized 1.5" thick , 18" square plywood pad under the jack, the gravel still settled funny under the jack and it must have still got torqued a bit because it starting leaking after that night and won't retract that last inch anymore. The leak is very small - just enough to wet the pad over a couple weeks. I've heard they are sealed and it's pretty extensive to replace the seals. So as careful as I thought I was being - it wasn't good enough.
BTW, I use a SnapPad on the front jack as it is harder to get my plywood pad under the center of the coach (3 jack design) and that jack has lots of ground clearance for the additional thickness for the SnapPad. Highly recommend.
