Personally, not being sure of myself opening up the motor, if it was mine I'd probably trade out the whole motor for another. If you are adventuresome -- you could part the stator and hub, and you could probably find a stator (or hub) to remedy the problem. Or, once open, the source of the noise might then be clear, and a solution will work its way into your head (and hands).

Again, though, I'm more of a Onewheel rider than a technician of Onewheel insides, and to me, to minimize board down time I'd swap out motors for one kept in my reserve jumble of parts for just this kind of situation.

Others in the OWForum here are more detail oriented!