|Noah I think you successfully narrowed down to the bearing issue. I would replace bearings to rule out.
Noah Britt wrote:
Update: I tried rotating the bearings 90°, but that didn't help much, if any.
There is some up/down play in the bearings; more up/down play than side to side, which was actually up/down once I rotated the bearings. When I say side to side play, I'm not saying front-to-back play, which can be fixed with fiber washers.
Does anyone know what could be causing the rattle? I think the bearings might be bad, but I'd love to hear anyone else's opinion.