I doubt it's the motor unless you've had continuing problems. Motors most often give more than one specific indication that the problem is in fact the motor.
The bearings, dust, and perhaps small chunks of debris can do exactly what you have stated.
Clean it good with compressed air, lubricate where indicated, and use a make-shift stethoscope (hose) to locate the area of noise.
Even if it should turn out to be the motor as long as you purchased it at Home Depot in-store or online and registered the product, there shouldn't be a problem with getting it fixed for free.
*Sorry- just saw where you didn't register the product. While registration was complicated several years ago, it couldn't be easier now. Upon submitting the necessary information (model number, serial number, and a jpeg or pdf of the order and/or receipt) I get back registration approval with a few hours. That's one of the reasons I typically buy Ridgid tools.
"What can be asserted without proof can be dismissed without proof." Christopher Hitchens
Last edited by sgcz75b; 02-06-2019 at 12:28 PM.