I put on my track wheel and tire combo after my Slingshot was sitting a few days and it started to make a really odd noise on each revolution of the wheel. I thought at first, that it was the sticky residue on the rear tire from the sticker, but it didn't go away. After looking closely with the rear jacked up, I found the issue...
The 20x12 wheel was balanced with wheel weights on the very inside lip. The weights were rubbing on the e-brake cable that was no longer in the sleeve correctly. See pic below.
If you are going to run 20x12, I suggest that you look closely at wheel weight placement. I also suggest that you make sure these cable are in the holders correctly and zip tie them so they can't get popped out.