I don't think it would ever be noticed. Despite the talk on here, attendings do NOT communicate at the level of what your talk was about two months ago. Also, you could be honest and say that this has been presented before but you might add more detail or a case that you saw on the current rotation. The letter writers at my home institution obviously mentioned my talk in my letter as it came up during a couple of interviews. This is about the only scenario that your talk would ever be mentioned between departments.
Almost every talk you have seen in medical school, whether a first year lecture or grand rounds lecture done by a visiting scholar, is a canned, oft-used lecture. Even talks at big scientific meetings have been done at many smaller meetings prior to your ears hearing it.
I did a different talk at different places because I tried to tie it to a patient or conversation with an attending at the place. I only did two rotations so it wasn't too difficult. If it is based on your own research like many choose to do, you have no choice but to repeat an earlier talk.