Serobot was right!  I have tried all the "fixes" to eliminate belt squeal.  And they all work, but not for very long.  Dust seems to aggravate the problem.  BUT if you go ahead and grind down the outside edge with a belt sander, the squeal goes away and stays away.  Thanks bot man.

I think ANY kind of spray makes the problem worse.

Harley belts are rubber, with Kevlar reinforcement... our belts are industrial grade... and pretty much plastic...
Tough as all get-out,... but they get noisy...

Have you tried more grinder?.... ...



"More cowbell!,... more cowbell!"... ...



I think the key is to get the edges feathered,.. keep it rough... never let it glaze...
Brutalize it... ...

Skin screeches on a gym floor.

Seems like a "Hand held Belt Sander would do great".   With the right angle the sanding belt would spin the tire/Belt.  

Its been so long ago I forgot how I did mine ?  

when I had my wheels off to get new tires, I took the opportunity to grind the edges a bit more.  I used a rasp and it did a good job.
Also, when I put the wheels back on, I made sure I had the right amount of "twist" in the belt, tension-wise.  It's been quite ever since, unless it gets wet.  But the sound goes away as it dries.

We lined up big pumps, drive wheel about three feet across, maybe four, pump, on the ground, drive pulley, up on the rig floor.
A rope across the end of the drive pull, pulled tight, showed us how to line up the pump. They used four to six belts. I used to drop old gloves on the belts, as they went down to the pump. It spat them out all cut up.

Anyway, a cord, poked under the belt, trapped by the front pulley, rolled forward till it's at the front, pulled thru stuff so you can get it across the rear pulley, it'll show you a lot.

Rember, the rear pulley is not a real close tolerance thing. What you see isn't likely to be exactly what you would see under acceleration.

When you are happy with the pulley s, spend some time looking at the tire /swing arm line up.