In the high pipe MC18 R5K / R6K there is an extra stinger or restricter tube in the silencer, I had one come loose and I spotted it sticking out the end of one of the pipe slightly, so I managed to pull it out. The pipe in the other exhaust took a bit more effort to remove, ie a big hammer probably. It was a long time ago, probably 2002ish..... It didn't seem to make much difference to the sound or performance?