If the rubbing only occurs when you are 2-up, you may be getting a slight twist in the swing arm due to a bad shock. If the shock springs and dampening are not equal, one side will rise faster than the other and put a little flex in the swing arm so the top of the tire goes to one side. It doesn’t take much.
Check the alignment of the swing arm to tire by removing the shocks and lifting the tire up into the fender. If the tire does not rub at that time, you may have what I just described. If it does rub, you’ll need to look further.
