I recently bought an SMB catback off black max which is yet to be installed. After lifting up the muffler (not a straight through muffler), there appears to be some clinking going on inside of there which I suspect are stones or little rocks or pebbles. Is there a way to remove these? Or is there no point? Will I be able to hear these little stones clinking around whilst driving/make a rattling sound? And more importantly, will it affect the performance of my 5/damage the muffler in the long run?
Any help would be muchly appreciated.

sliq.