It is hard to get a direction on a noise when riding a bike. V Twins make a lot of noise naturally. If you can have a jack or can get the bike off the ground safely. Try spinning the wheel by hand, its not the same but you might get lucky. Don't rule out the front wheel or a rattle. Stress the bags and mounts, look for something moving,have a look at the belt tension. If I remember right 10 lbs of pressure on the belt should flexx it up one inch. Don't rule out a squeaky seat, luggage rack, sissy bar,fender, all that neat stuff.
Take a look at the brakes, test them while spinning the wheel. A brake pad could be the culprit. they do rest against the disk.
Good luck, you may get lucky. Its not the same as riding though. Don't take a chance of dropping the bike if you don't have a jack be careful.