There have been issues with pre-facelift models of mirrors vibrating resulting in the noise that you describe. The issue has more often than not been resolved with Mazda replacing the mirrors for those fitted to the facelift models free of charge. In your case I would suggest that Mazda getting involved would be very much dependent upon what, if any, guarantee (Mazda or dealer offered) remains on the car. Either way it won't hurt you contacting the dealer advising that this is an issue known by Mazda and take it from there.
Incidentally, in a few instances replacement mirrors have also caused a few owners issues although this is limited to extension mirror use when towing. Owners have laid out a fair bit of money on very expensive extension mirrors only to find that they do not fit the new form that the facelift mirrors take.