You basically have 4 ways it could
Vibe.
Axle bent/not centering
Bearing seat not fitting correctly (angles the bearing a little, or not secured well),
Or an actual imbalance between the two halves due to damage, poor quality, etc.
The most common Ive seen is the axle threading isn’t to a high enough tolerance so there is “wiggle room” which causes vibrating.
You may also have issues with the actual bearing. The inner or outer races could be bent, a ball damaged, etc.