Rear Tire Groove

[BimmerETC]

I have a 96 328i convertible with just over 103K Mi on it. Lowered suspension (done by a prevoius owner), 17" wheels and 235/40-profile tires. During a recent inspection, it was noted that the right rear (and to a much lesser extent the left rear) had worn a 3/4 deep groove at the inside edge of the tire. I've had this car fro years, and rotated the tires when I did brake pads/rotors about 3000 miles ago. Never noticed that groove until recently. Could this be bad shock mounts? I don't hear any rattling, nor does the rear feel funny when cornering. I'm not sure how to visually inspect the mounts with the convertible (no speakers to remove!).
Could something in the susp. system have moved, and now it needs an alignment?
I'm afraid if I simly replace the tires, it will happen again unless I find the cause. used

[YoungExec728]

if it was the rear shock mount you would hear a loud knocking sound coming from the trunk