A month ago I was grumbling about many of the K5/K6 fuel tanks being discontinued. I now see that the exhaust pipe is gone too. You might keep an eye out on ebay for a good used system. Webike offers titanium systems by Tsukigi Racing. As it's built to order, you might be able to get some customization. I'd expect the noise level to be more associated with the muffler than the exhaust pipe.