How to determine if motor bearings are going bad?

[TDKPE]

I have a "mechanic's stethoscope" that lets me listen to the noises from certain areas via a metal probe so I can easily listen to the suspect area.  

really helps me locate a noisy bearing, but wouldn't help if quiet is the problem

The OP can stick a big screwdriver on the bearing housing or cap, and his ear on the handle, and possibly hear the bearing spinning the blade by hand.  Old-school.  Not as good as a stethoscope, but definitely better than the unaided ear.  Especially my ears.  

[John Mihich]

IMO - don't worry about the bearings.  You don't have an electronic stop so the blade will spin; lots of force on the blade when power is shut off so it will spin for a while.  You will be able to hear bad bearings.