My 2012 S60 T6 (built in September 2011) had a problem of wind noise and whistling from the passenger side-view mirror at highway speeds or seemingly from around the A pillar. The noise was most noticeable when driving in a cross wind. This is a known problem.
The dealer's service department replaced the seals around both side-view mirrors and the problem was immediately solved. The tech bulletin listed in this thread is correct RTJ 23725. The current part numbers for the seals to fix this problem are 31335274-1 and -9.
I know how difficult and frustrating squeaks, rattles, and noises can be to fix. So it was very helpful to get information from this forum that confirmed that this is a known problem with a fix. The dealer went right to that fix. Otherwise, we end up going through trial-and-error process until maybe we find the right solution.