reverting to stock actually puts on Cobb's version of the stock map, so its possible it might be a little more aggressive. Its also possible you have a leak somewhere making it louder.

ps, the dealership can still see you've modified the map even with the so-called stock map Cobb gives you. But thats only if they look for it. Better then leaving stage 2 and letting them know you've up'd the boost, though.