Exhaust pipe rubbing the shock!

My bike (sp1) came with these foul "predator" exhaust pipes. I noticed that the pipe was touching the shock after buying the bike and set to moving the pipe away from the shock. Everything has been ok but I notices today that the pipe had made its way back to touching the shock. Has anyone else suffered this with other pipes? Is there a fix? And...what pipes would you recommend on a budget?
Cheers
Cheers