Chasing down a roar, all the usual suspects ruled out.

[Hardline]

03 Expy, 168K miles, 4WD

Roars when going straight or turning right. Louder when turning right, about disappears when turning left. More noticeable with A4WD engaged.

Parts replaced

LF Wheel Hub x2 times (second time needlessly, thought it was a bad part)
RF Wheel Hub
LR Wheel Hub
RR Wheel Hub
Front driveshaft u-joints
Rear driveshaft u-joints
Tires

I'm now thinking it is a carrier bearing in the front diff.