You have to remove the tranny and clutch to replace the rear main. 3 hour job with a lift so a hundred bucks is a good deal. The noise you hear could be an aftermarket fly wheel and clutch if you bought the car modded or could be something loose have that someone that changes your seal take a look for you. But if you heard the same chattering noise before on another car that is normal chances are you might have a aftermarket flywheel/clutch.