Worn shocks and/or struts will cause cupped tires. There may be another suspension or chassis component worn, but the shocks/struts are the first components that should be inspected.
Lack of rotation, aggressive driving, or a worn steering/suspension component. Check the tie rods and ball joints.
Bad alignment
Yes. More than likely there is also some kind of mechanical issue as well, you need to get this fixed or the same thing will happen to your next tires as well.
might want to check your drums
the tires themselves.
yes 13000 miles both front tires inner wear.running 35 psi
will tires make noise if there choppy on inside
tires
If the tires are properly balanced plug tires should not cause a vibration.
Misaligned axles, bad mounts on the tires, improperly inflated tires.
FRICTION
Overinflation.