The rim drive belt MUST be perfectly seated in groove of the rim drive to avoid out of true energy being transferred to the tonearm. Here is a little trick that rim drive users have used with great success.
Take the belt off the rim drive and take some fine metal polish and polish the rim drive groove in which the belt rest. Brasso metal polish works well.
Once polished, take some car wax and apply and polish the rim drive belt groove.
Take the rust colored belt and boil in water for 2 minutes. Dry the belt and reinstall back into the rim drive. Be careful not to twist the belt when reapplying.
Take a round metal or hard plastic object (a bic pen works well) and gentle run it over the belt to seat the O-ring into the groove.
FIRMLY position the rim drive against the platter with and run at 45rpm for 20 minutes.
After 20 minutes, readjust the rim drive so that it just touches the platter. As a measure of appropriate pressure, the platter should spin 2-3 time when the drive is turned off.
The polishing of the rim drive belt groove allows the belt to seat properly in the groove correctly.