Lately my 1988 ford Bronco, with a 5.8L engine and c6 auto transmission, has been making a loud thunking noise while driving. I can feel each thunk underfoot in the driver and passenger seat. This usually occurs while coasting but occasionally also while accelerating. I do not have much experience with transmissions or u joints on drive shafts but those are the places I would venture to guess the problem is. Any advice on where to start diagnosing the problem would be appreciated.