Thanks, Apple. I listen to the headphone jack out with some very sensitive IEMs (inner-ear monitors)... anything above 1 click on the Mac's volume and it is too loud. Half volume on these would probably be deafening... so I stick to 1 click up. On my old 2008, there was a horrendous noise floor at that volume level. On the 2011 there is still a bit of hiss and hum but it is much, much reduced.