My car did that when I had GNX style wheels and wide (245's) tires on it. It seemed to follow every rut in the road. I got less obvious when I switched to Weld wheels and 1 size smaller tires (235's). The biggest change was when I aligned it.
Check the RS upper control arm bushings, and have yer alignment guy set it to the effect of .1 neg camber, 3* pos caster, and ..05* pos toe and see how it feels. Make the caster as equal on both sides as possible, dont do a cross caster diff for crowned roads like the spec probably says, I think that causes a drift and usually take that cross caster out of my alignments
Wearing the inside edge of a tire is usually toe out (or negative toe), but can be camber too.
Fortunately for me, I have the luxury of playing with my alignment angles, where you might have to pay for it. Those numbers seem to work nicely for me. Just one thing, positive caster gives stability and makes the wheel return to straight but too much can cause a shimmy. Caster is NOT a tire wearing angle so dont worry about adding some to the factory spec. Toe and Camber are tire wearing so I like to stay close to spec on them, but will vary at times according to what the tires are doing, or in the case of my cars, the right "feel"