2004 Chevy Suburban Rear windshield wiper motor

There's a "clinker in yer thinker". If you're hearing knocking, the motor is running so nothing is shorted. This would be typical of a linkage that has come apart, but there aren't any linkages for your system. It's all built into the motor / gear package assembly. The size of the motor assembly isn't very substantial, so it stands to reason parts inside it are going to break, especially if the gears are made of plastic. Was that a used motor you installed? If so, it likely has the same problem as your old one. If you bought a new motor assembly, be sure the wiper arm is bolted tightly to the splined shaft.

Also, if all you replaced was the motor that bolts to the assembly, the problem is in the gear package, not the motor itself. Those are about the only possibilities as the entire system is self-contained.