And there was much rejoicing in the land! The raspy buzz is gone! I put on a used header pipe from a low-mile (2700-ish) 2013 F800GS that I got on e-bay from somewhere in Canada, along with a new O2 sensor. Getting the old header pipe off was a pain, but the new one was surprisingly easy to get on. I didn't remove the radiator, and there was *just* enough room to get a deep-well socket in there to remove the nuts at the exhaust ports, with some gentle encouragement on the radiator to keep it out of the way. Naturally, none of the reverse Torx sockets I had in my toolbox fit the exhaust bolts, so I had to buy more sockets. But to make enough room to get my hands near the cat to unplug the O2 sensor, I removed my chain guard and ended up trashing it in the process. The center bolt was coming out nicely, but out of nowhere the head stripped badly. I ended up having to cut the chain guard, and there is now no chain guard on the bike, and a damaged bolt that I still need to remove. Meh...I'll get a new chain guard, and the O2 sensor plug is now ziptied in a much more accessible spot. While I was at it, I installed new handlebar switches (the old ones were faded and sticky in operation from the previous owner apparently parking the bike outside a lot), and installed LED headlights.