Have the wheel bearings been checked. My bearings started making noise out of no way one day. I checked everything I could think of and get too. Removed wheel and check cked bearings. They seem fine. Replaced with aftermarket that a friend got locally and all was fine for about 500 miles and the noise came back. Removed wheel again to remove driveshaft (which was new from Triumph) and check it. Found I did not press one bearing all the time way in due to a burr I made when removeing the old ones and missed. Ordered new bearings and seal from Baxter's Triumph and reinstalled. No problem so far and about 4000 miles. I may have miss aligned the differential to swing arm and wheel. The differential nuts need to be snug then the wheel put on and axle nut snugged up. Then torque the diff nuts down then the axle nut. A little play here and there addes up and will put something in a bind. Trying to check bearings with a load on them can be hard to due. They may seem fine but are in fact bad. Get a hold of Technicians stethoscope and try checking with that. You will be surprised what you can hear with it.