check the tranny fluid if you haven't done that. the fact that when you put it in neutral and it gets quiet would make me rule out a exhaust leak. If it was the exhaust it would do it whenever the engine is running. BTW, How mechanically inclined are you and how many miles on the car? I would put the car up on 4 good jack stands and first crawl under the car and give a listen and feel to your exhaust system. Check for the sound of air escaping the pipes and you should feel puffs at the leaks. Then run the car through the gears on the jack stands, BE VERY CARFUL WITH THIS PART, make sure a friend or two is there to help. Pop the hood and listen for noises from the transmission from above. If you feel the car is safe crawl underneath and feel for and check the exhaust with the car in gear, park, and neutral. Look in the forums for your locations and post there, I'm sure a local would be willing to help you diagnose the problem if you are unsure. Hope this helps.
