Right off the bat, let me say that I have never experienced this nor do I even have any reasonable (meaning logical, thoughtful) guesses. That said.....
You are correct in that the entire final drive, the bevel gears and 1/2 of the clutch all spin with the rear wheel. The rest of the clutch and the entire engine and transmission do not. Unfortunately, often a gear while will only sound under load so it may well be the final drive and the reason it quiets down when you pull in the clutch is because all load is removed from it, not because ti stopped turning. Running gears that are badly worn often show a line or ridge, and that is the cause of the noise but again, only under load.
The only thing that may be useful that I can think of to suggest would be to either have someone else ride with you, move around and perhaps lean over each side fo the bike enough to try and find the side of the noise source. Another thing might be an inexpensive mechanic's stethoscope with the probe removed so only the hose is left; pointing the end of the hose around should home in on the source of the noise pretty accurately.
Of course I realize this must all be done at highway speeds and so do so safely, perhaps including strapping the passenger to yourself while riding so nothing terrible can happen.
Last idea is to run the bike on a dynomometer. Unfortunately almost all of them in existence are DynoJet dynos, and they are not 'real' dynos capable of putting a load on the bike at a steady speed. Still, a DynoJet dyno would allow you to repeatedly power the bike up through that speed range while others stood and listened for the noise; it should not take very many cycles to find it as you describe it as a howl.
Best of luck with this....
Brian
I searched around, and though I found some discussions related to the clutch and final drive, I haven't found any discussion related to this particular situation.
So, regardless of gear (I've checked 4, 5 & 6), when my Connie is at 75-80 mph, there is a loud howling noise that seems to be coming from the engine/transmission area. If I back off or speed up over that range, the noise goes away. While it's howling, if I pull in the clutch lever, it instantly goes away. This is why was hoping it could be related to the clutch and not the final drive. Considering that the final drive is always spinning at the same rpms at 75-80 mph and the clutch isn't because I've tested this in different gears, I'm thinking that it might be the in the FD. Otherwise, the bike runs flawlessly.
Has anyone ever experienced this?
Thanks guys,
Ray