Guzzi is one great bike shy the gear box whine, I've worked on a handful of Guzzi and almost all of them have it. It does seem to get louder as the bike gets older. Keep a GOOD oil in it and shouldnt have any problems. Amsoil makes some of the best motorcycle oil i have found and that would be what i would run in it. During your next oil change check out the gears while you have the pan off to change your oil filter. Everything is easy to see and look at. If there is anything else i can help with or if you have any more questions please feel free to contact me
M. Woodring