I'm getting this muffled rumble from my tranny and i haven't heard it before. it started after 28k miles. is this a normal characteristic of my car? oh and its a 6mt. i'm also hearing a hissing noise from the rear of my car, kind of like the noise you hear from mercedez-benz's. any help on this would be greatly appreciated. i don't want to take my car into the dealership if there isn't anything wrong.