Interesting.They've done a really good job if he's working on the other side of the hill, so they have the ability to at least partially adapt (they no longer care about the heavy air traffic or loud guns either). I think part of the problem is that they can see it and feel the constant rumble. I have a 90% shade cloth on the back of the run for this reason. Can barely see through it myself, but they start alert calling as soon as the guy walks up there.
I tried sitting out with them for an hour yesterday. Brought special treats to try and get them foraging. They just stayed huddled in a ball, or ran back and forth trying to get away. Broke my heart, so I brought them in. This one's a tall order. The equipment is very, very loud and overhead from their POV. Like an aerial predator from hell.
Any chance of moving them to another part of the property temporarily, instead of in your basement? I'm thinking a portable run or "pet playpen" put somewhere else.
Or maybe consider building an actual coop & run on a different part of the property. You can work with a slope: just build things up at the low end, until you have part of it flat enough to put a coop on top of. Chickens do not seem to mind spending time in a sloping run. If you make a roofed run, the slope of the land may even make the roof slope for you to shed rain, without any effort on your part.