My friend rides a KX450F and he says that after 6 weeks of having the bike it got really loud and he had to repack it becuase he burned all the packing away. I've had my for almost 2 years on my 250f and it hasn't gotten any louder. He does hall the mail around the track and would smoke me any day. But can you really burn all the packing out within 6 weeks!?