offset shouldnt matter.
the wheels are tight against the hub? and the lugnuts arent bottomed out? (open or closed lugs?)
I'm betting on wheel balance.
yo can easily check the out lip of your wheels, there should be a crimp on weight on each wheel.
May 2014 ROTM
for auto-x: '04 Liquid Grey ZX3
for street: '02 Infrared SVT