97 Honda Accord making a banging noise?

I dont know if its my tranny or what but whem im driving i hear a certain little bang i can feel it on my floor board when it happens i thought i was my muffler but its only a yr old and it sounds as if some one is under my car hitting it every so often with a small pastic end of a screw driver lol i know bad way to say that but it sounds from the rear but i feel it at my feet so i dno tranny or something going lose?? I looked under the car but nothing is draging.. confused..