Had my new 2013 Macbook Air 13" base model for 2 days now and everything has been great aside from the speakers. When watching a video, the speakers seem to automatically drop their volume intermittently. The sound will be a constant volume for a minute, and will then drop to half the volume of what it should be, before reverting back to the normal volume after 20-30 seconds. There is no on screen volume indicator when this happens (i.e. it is not showing on screen that the volume is changing). Anyone else having this issue?