If it always does it in the same place there may be other possible problems. As a test, remove the belt, position the tonearm just before the speed change occours, spin the platter by hand and then lower the arm onto the record. If the platter does not spin freely, it is a bearing problem or the bottom of the platter is making contact with the plinth. Likewise, if you still hear the speed change, though spinning by hand will not yeild 33.33 RPM, you still may be able to hear it, then it is not the motor and other causes must be looked at. Leveling the table is very important and may also be a consideration. Finally, the good folk at SOTA are a wealth of knowledge and are generally willing to go out of their way to help. They would be your first resource.