This is true, in the Pittsburgh area there are patches of public / private land, lots of it, between developments and suburbs. Like the South park dumps, even where I rode Trax Farms. I used to ride a coal path that went from Library to Peters (the old Montour rail, which is now an offical walking path) and it was right behind houses and under overpasses.
Truthfully, Jetz is right out here the riding areas are in the boon docks, if anyone lives out there they are like the people in "The Hills Have Eyes".
They don't really enforce the sound in the woods as much as I heard they do out in the Dunes areas. But still, the woods are shared with Bicyclers, Hikers and Campers so even if no one is living there you have some one taking a video of an eagle taking a crap on a deer on a hiking trail it may be interrupted with the sound of 2 stroke and he may complain. So even out here there is a chance, even though slim, because if your bike is louder than 99db and they check they can give you a ticket.