I sure hope someone can help. My wife's Navi has a nasty sounding vibration under load at 1700 to 1900 rpms. I know this is the "drone zone" for this motor, it's our fourth 5.4, however the dealer can't identify it. So far they have replaced the mounts for the tranny under some internal recall. Then they recentered the exhaust by loosening everthing putting it in drive and then retighten. Next they replaced the resonator. Now what?

Like I said it is under load, doesn't seem to matter what gear and can get fairly loud sometimes. It seems to come from the rear area. In addition it may not make any noise at all, but then you slow down or maybe turn a corner and you will hear a little sliding clunk, at then it vibrates.

I am guessing something to do with one of the half shafts or rear end but I don't know. I am reluctant to take it back in for the fourth time. Any suggestions?