Not sure, but from what you describe and if they look like the pic below, your pipes may have had MarkT's exhaust mod performed on them.

(photo taken from Mark's website)
The removable pipe is called the trombone and can be taken out to get a deeper sound. I have a set of Mark's modded exhaust and I developed a rattle also between the trombone & glasspack. I shimmed the gap with some smaller metal fender washers (bent semi-circular) so they'd slide in real tight, but with enough lip hanging out to grab onto with a needlenose. Eventually though, I removed the "trombones" completely as I like the deeper burble.
I can't be sure Mark performed the work, but he's a great guy to work with and here's his website if you want more info on his stuff:
http://www.horseapple.com/Valkyrie/Valk_Products/M2W_Exhaust__System/m2w_exhaust__system.htmlNot affiliated, related to, stand to inherit from horseapple, yadda blah etc...
