You don't have to touch them for them to be loose. Did you put a wrench on them and give the bolt a turn?

Can you replicate the noise if you rock the truck back and forth from outside? If so your Watts linkage bushings may be shot. I included a pic of the watts.

 

I've had that sound and it is not the sound of shocks topping out.

It is a sound that happens AFTER you go over a speed bump and the spring releases so powerfully as to slam the wheel/tire back down to the ground abruptly.

I have 2" lifted springs and standard length shocks.

I was advised by the most reputable dealer on this site that 2" lift springs do not require +2 shocks. Only over 3" lift requires the +2 shocks.

 

Sounds like watts linkage bushings/bearings.

 

I had this happening to me after I installed my lift... it was my rear shock not being torqued down correctly and it was moving around every time I rolled over a grain of sand. Tightened the bottom bolt and it went away.