After I had the dealer replace one of the rear struts for clucking noise (TSB). I have been getting a very slight "clicking" noise from the back seat

The noise is on the passenger side of the rear seat. It sounds like 2 metal keys tapping a little bit.
The noise goes away when anyone sits on that side of the back seat, but is still there when someone sits behind the driver.
Its definatly coming from the top side of the seat (Near the headrest, but almost more toward the center of the back seat (near the sub))

I have removed the headrest, and tightened the bolt behind the seat and it helped for a few days, but it now is back..

It is somewhat intermittent, and usually happens on smooth roads (interstates)..but so much on large bumps).

Any ideas other than that one bolt? Is there something behind the seat that can be loose? Its not anything in the trunk area, I felt around the pass through slot.

 

make sure that all the clips that hold the cloth covering for that shelf are properly inserted, the shelf cover needs to be removed to install new struts.