HELP! I'm running out of ideas

How have you checked your alignment ? If your toe is way off, you could be dragging your wheels in a turn. I would get that done first . Wheel bearing problems are usually shown as a loose wheel from adjustment not being correct , or worn which you can see as pits in the bearing and race causing a noise that is audible that would match wheel speed. Differentials not releasing can cause problems if you have a limited slip on a turn , Wheels spin at a different rate in the rear and show up as a bad vibration during a turn. Angles will be different in the front on a turn with ackerman that could multiply an issue not showing up going straight.