I don't have a belt drive but I did manage to google this:
Rear belt drives on Harley Davidson motorcycles can make noise due to dust, mis-alignment, bad tensioning, and wear. Correcting these problems is an easy task that most owners can do themselves.
Replacing the oily rear chain on Harley motorcycles with a clean, efficient belt drive raised Harley-Davidson motorcycles to a new level of comfort. It also reduced maintenance greatly. When adjusted properly the new rear belt systems can last 50,000 or more miles with a minimum of adjustment.
One complaint we do get about them is belt noise, usually a squeaking or squealing sound caused by the belt rubbing against the inside or outside of the pulley. This noise is caused by friction and can indicate that maintenance is necessary.
Since the belt is not completely enclosed, a trip down a dirt road or a ride in a rain storm can cause bits of sand and dirt to embed in the rubber belt. These bits of dirt are harder than the surfaces they are rubbing on and cause the squeal and abrasion that will eventually cause premature wear on the motorcycle belt and sprocket surfaces.
The cure for this is to put the motorcycle up on a stand so the rear wheel spins freely, and wash the belt and sprocket off with a mild soap solution. I like warm water and a small bit of Dawn dish soap. Use a rag to wipe the belt off as you rotate the wheel, then rinse with clean water. Let the belt dry thoroughly, or blow the water off with compressed air. Many times this is all you need to do, but for really squeaky belts you can spray the belt lightly with Dry Silicone Spray by Krylon that you find at the hardware stores. This will quiet the squeakiest belt.
One other thing to notice is that the belt should always track to the outside of the front and rear pulleys. If you roll the bike backwards it will track to the inside and sometimes squeak as well. This is normal because Harley Davidson designs a slight angle in the transmission pulley mounting to keep the belt tracking to the outside. Make sure the rear wheel is aligned correctly and that the belt tension is correct as outlined in the motorcycle service manual. I don't recommend using any type of commercial belt dressing, they are designed for friction belts, not for tooth belts like the Harley Davidson type, and because they are sticky they will cause dirt to stick to the belt.
When your motorcycle belt is clean and well-adjusted you'll have a quiet and reliable drive.