Process of elimination right side detection:
1. Belt ~ as mentioned, you can spin the back wheel, soap or chalk the top of the belt as a staring point. Say, from the bottom of the wheel, move it to the 3 o'clock position, mark it, start a the bottom, back to the horizontal 3 o'clock. Why? Pinpoint rub. With a paper towel rapped around the index finger, swab from mark to mark. If it's not obvious that belt thread is sticking out of the side of the belt kind of 'there it is'; you can see where that dirtier point to point was, meaning, a hint of material loss on the finger pass.
Then, the who knows how many times is the 360 of the wheel, it's not like rub-rub every 360 degrees of the wheel. Or will it with wheel off ground? But say it takes more come-around where we have a combo of many wheel spins before the rub makes the noise.
2. Bearing ~ as mentioned by a few, say we retract the rear brake pads away from the disc. Eliminate this for a few reasons. One is the failure to find the squeak at the belt with the retraction. Failure to find a bearing failure. Then, with a test ride after belt/bearing showed no joy. Say the left side might throw a curve ball at the noise, where you eliminated the [possible] brake squeak. All you did was check without a belt adjustment or a wheel removed for a bearing check. Noise still there, then pump the back brake up asap. Can't stab the pedal by accident in test mode. Belt/bearings/pads is the loop, unless I missed something.
So a static bearing check with the pad retracted in play, hands at 12 and 6 o'clock. At the same time, push out 12, pull in 6. Go back and forth is X. Hands at 3 and 9 o'clock, same push and pull is Y. With the belt marks numbered 1-2-3-4, start at 1, go back and forth till you see 2 at your starting point, place 2 at your starting point and watch 3, and so on is Z.
3. The deal on this one is exactly what you don't want to happen is a new belt to tooth pattern. But I do not know the history of tire changes and the tooth to tooth timing of the original matching wear of new belt and new sprocket. No mark where tooth matches with tooth, then here is where it's not side to side, meaning, wheel not square to frame kind of angle, but tooth over tooth pattern setting in. So, last time tire was changed and was the belt to sprocket marked? So it's no joy at finding a static squeak at the belt, no bearing showing itself, no retracted pads on the test to see if it was the pads. The last resort is to pull the wheel, hand feel the bearings, move one tooth off of the timing of teeth, test ride and did the squeak disappear? Could be tooth ride up.
