I'm definitely no expert....
but I'd start with the same idea - try running the motor sans belt. Is the noise the same in spin and agitate?
Also, try turning the belt by hand in agitate mode, it should be fairly easy to do without a lot of resistance. If it seems really stiff there may be some other problem and in that case I'd look at the pump first.
If it checks out OK the motor could need to be lubed which isn't too bad a job. If you take the motor off take a picture of how the brackets are oriented before disassembly to make it easier when you put it back together.
Congrats on these great finds Phil!