I suspect "sound shots" are more myth than reality. I know PA as well as anyone and haven't seen these supposed sound shots.
Seen them by PA hunters in NY, MD, and VA; different people, different locations, different years. YMMV, obviously, but when a guy fires a box of ammo from the stand in a single day and says point blank that "I didn't see anything, but got off some good sound shots but don't think I hit anything", it's a pretty good indication of what he's doing. Never encountered it from hunters from any other state.