I switch my wheels/tires when I go racing. Last time I came home and left the ET Streets on for a week or two while the car sat in the garage. The next time I drove it I was getting bad vibes from them. I took them to be balanced and the guy showed me that the tires weren't exactly round any more.

Do slicks really get messed up that easily? Should I put the rear on jackstands every time I park it?

 

They should be OK after driving it for a bit....that's rather odd.

 

My friend parked his for like 8 weeks with them on and they were fine after a few miles of driving and a good burnout.

 

It sounds like they just flat-spotted. Like was said, some driving and a bit of a burnout will take care of it.