Trouble with rega white belt seating properly

It probably has to do with your motor being seated properly.You have to take off the belt loosen the screws on the plinth that are either side of the pulley.Then pull the motor down so the top of the pulley is centered and lower than the sub-platter.Tighten up the screws and put the belt back on.It should be fine now.

If you have the old motor suspended by rubber belts the screws at the plinth if loosened enough with right sized allan key(3 turns approx.) will allow you to reseat the motor.If of course the rubber suspension belts are not worn (replaced these once).I have had this issue myself and it is not cured until the Rega motor sits correctly,never had to return a belt.Don't worry about fiddling here it won't destroy anything just make sure the arm is locked down.The top of the pulley must be lowered to stop the problem you describe of the belt riding up.I got the tip from Vinyl Asylum initially and it has always worked for me,I believe it is the Rega "official method" for this issue.

The suspension of the belts holding the old style motor eventually wears out.I obtained replacements for these on English ebay,search Rega.This is a bit fiddly!You have to remove the motor cover under the plinth.Your belts could be o.k.just make sure they are not caught on anything and manipulate from underneath (screws loose) with power off,platter removed etc, just center the motor and pull down. Stretching the belts down within reason is o.k they are fairly resilient.Make sure top of plastic pulley is lower than,and centered with the sub-platter(platter off)then retighten screws and replace belt.Replacing the motor belts is more difficult,I took the motor right out and forced the new belts through the small gaps on the side of the motor.The new motor upgrade I personally ignored,I just replaced the capacitor and resistor on the circuit board with new ones and put new belts on.You might not have to replace the motor belts anyway so it should be fairly easy.