Does it only rub on the chainstays or is there anywhere else it rubs? Are you sure you have got your wheel dead straight in the centre? As it shouldn't rub at all. If your wheel is dead straight in the centre, they you may possibly just have to wear down part of the tyre... with a file or something. It shouldn't rub though so there must be another problem with your setup i suppose. EDIT: Just looked above my post, It should't be time for a new tyre already because he said he just purchased it meaning its pretty new anyway. But yeah, I suppose if there is a buckle in the wheel that wouldn't help things.