2010 F 350 6.4l diesel rear suspension problem

[SHOWUUP1000RR]

Okay I have a problem with my truck and I took it to my dealer and they cant even figure it out so maybe someone has incountered something similar. When I drive over a pot hole or rounded curb like at the end of a driveway at about 10-20mph and my left rear tire hits and the suspension compresses and right when its rebounding it makes a hollow thud type of noise which is pretty loud almost like something hittting the under side of the bed. When it makes this noise I can also feel it in my feet. I had them look at the rear suspension but they said it all looks good . Anyone have any ideas