My w56 started making noise in 5th gear. Then 4th. Started out only at freeway speeds, then eventually all the time. After that it blew up. A good tranny should make no noise. I have one now that doesnt make a sound at all.
do you actually feel a vibration in the whole truck: your seat the floor and dash? or does it just make grind and or whinning noises only in 5th gear? yeah a good tranny shouldn't have much noticeable noise