I would be very careful about this. You need to understand how your PD generally responds to resident transfers and make sure no one else in the department is aware of this. If your PD has never allowed residents to transfer (for whatever reason), you would be well advised to finish and considering switching after that point. Otherwise, if you know he/she has been supportive, I would approach them as soon as possible. Be very careful not to upset anyone or make it seem as though you are not conducting your clinical/call responsibilities (leaving anyone short-changed). This comes from personal experience, programs will do anything possible to discredit a resident who "burns them" by leaving an opening that could potentially go unfilled. Suddenly your evaluations are not as good anymore, etc. (you get the idea).