I think your experience will vary from Walmart to Walmart in your travels as to generator use. We have a Walmart Super Center about 2 or 3 miles from our house, last year an RV set up camp there for 4 or 5 days (nights). Slides out satellite dish deployed (generator running) and IIRC chairs out too! NOBODY in the duration of their stay said a word to them about THEIR practices. If they had the Franklin Police would've "escorted" them off the property I'm sure. I thought that was pretty "bold" on their part to stay that long using a generator but that's just me. A lot of trucks stay in that section of the lot too, they all "seemed" to get along.
Listening to a loud generator all night long would definately annoy us, we have a Honda inverter style generator we sometimes use when boon docking, with it running at the rear of the trailer we CAN'T hear it in our bedroom. Last time we used it at a park in the UP (Michigan) we had tent campers staying about 100 feet from our site. After starting it up I walked over to their site to ask them if our generator was annoying them, we couldn't hear it from there, they didn't even know I had started our HONDA up! :B
Dan