A casual observation...

[Flight Test]

I was on the way to my local Lowe's when I came up to a fairly new Chevy 1500 Silverado extended cab with the four doors. (I thought Chevy introduced this model within a year or two?) I was behind and to the drivers side when it passed a sunken manhole cover. What caught my eye was how the bed shook for a second or so. I think the current GM light duty truck platforms still use an open "C" channel frame, someone correct me if I'm wrong. Just wondering how much this architecture, if any, lends itself to this bed behavior.

[TOK]

Sounds like maybe you missed the bump, but you might have seen your Titan do the same thing. I've seen my bed jiggling in the rearview over bumps.

[PTitan]

I believe the Titan and F-150 are the only two trucks that use the full box frame (Toyota is mixed box and C-channel). All others use C channel. It may have added to the visual effects when the Chevy hit the hole. I am sure the Titan would have resulted in a similar effect.

[DeTitan]

I ditto TOK

I believe the reason for the caboose and the bed being two pieces is so that the truck bed can shake rattle and roll.

Your titan does the same thing as the gulp silver-ado oh oh now I have done it.