Jack up the trailer so the wheel is off the ground. Once the wheel of the trailer is off the ground spin the tire and wheel around by hand and see if you hear any roaring or grinding type noises.
If you hear any roaring or grinding type noises then wheel bearing is either bad or is about to go bad.
If you hear any of those sounds it's best to get new wheel bearings as you'll likely be repairing the wheel bearing on the side of the road if you don't and you'll lose your wheel and hub and might cause a deadly crash.
You can also move the wheel back and forth to see if there is any play in the wheel bearing. If there is play in the wheel bearing you should pull the bearings and check them.