Found the source of my rattle

[papageoff]

Just now, papageoff said:

Agreed.  I'll do some digging and see what I can come up with.  Maybe it'd be enough to get a bolt and washer just big enough back there for clamping.

 

Also, I could put some other bolts around the patch to reinforce it.

[schmolf4]

My company provided dodge ram had a set of aftermarket steps and both sides ended doing the exact same thing.  the aftermarkets mount into the thin metal of the backside of the rocker panel.  I cut 6 4"x3"x.25" pieces of aluminum and screwed them into the rockers then secured the steps to the thicker aluminum.  they were like that for 2 years and they never moved since they were reinstalled by me...