It could be the bearing or an object popped into the motor casing. Rough roads could wear down the bearings fast. See if the main motor shaft wobbles. The motor case can be taken off with some screws and a lot of force (fighting magnetism). I’ve seen a few YouTube videos in past years of people stripping their motors to clean.
An aside and adding to the thread, I am a Sacramento transplant now living in Philly and have gone through a DIY build. I’m working up to a V2 soon, taking learnings from the first round. I must say, these Philly streets are rough on my board. I’ve managed to cracked the battery enclosure twice in 3 rides!!! Cheers to DIY esk8.