So I have installed the RTe 4" kit with fox Shox. The rear end of the truck has this crazy loud rattle. The front seems fine. I used the fox provided spacers and washers outside of them to try and space the proper width in the shock mounts.

Could these spacers be causing the loud metal rattle? Is this common or am I overlooking something?

 

Just a guess, but I bet it is your exhaust pipe touching your rear frame cross-member. Or something close. Mine rattles sometimes, I used a piece of pipe strap to hold mine from rattling.

 

I talked to RTe and it seems that it is the metal heims used on the fox shocks. I called ORW and ordered some poly bushing inserts to replace the heims.

 

I too did this. I bet half of those spherical bushings were sloppy, and from little use. The poly bushings work great and I haven't had any issues with them.