Right you are Candace.
The black rubber band belts are OK for temporary use if your real belt breaks or dies on the weekend and you need to keep sewing till you can replace it Monday.
The sad thing is my ALDENS Magic ZZ machine has a stationary motor with zero adjustments. At first I thought it was a home made replacement, but when I studied the pictures in the owners manual the motor is original. And the pics show a rubber band belt. Guess what, it hums and buzzes and struggles to go. With no adjustments I'm pretty much stuck with the rubber band belt. Yuck.
Joe