[24boosted]

What can I do to fix this, and is this a huge problem?

Yeah check the integrity of the wheel/hub, get a better place to balance the tires. Check if your lugs are tightened to the proper specs, might be loose.

 

[24boosted]

My tires right now are 245-40-18. If I bought a smaller set of tires, would the rubbing go away (considering they barely rub right now)?

Get some 215 or 225s stretched and you should have a chance the tire sidewall will be set more at a lower angle. 245s are way too wide. I have 245s on my 350z. There are a few members on here running lower offsets. I'm one of them +32 on 18x7.5, +30 on 17x7, 17x7 +37 - 07 Si. But my tires are 215s or 225s.

I tried my 18x8 +22 offset wheels on my Si didn't even try driving on it though.