As I was demoing a bunch of headphones tonight, I discovered something rather surprising: the Yggy reveals this sort of tape hiss. At first i was wondering if it was some feedback or interference with my interconnects. As I played more tracks, there are some tracks that had it and some that didn't I thought it was an MP4/FLAC thing and so I compared the same song back to back and the hiss was there regardless. Then on some albums the hiss changes from song to song (see: Iron & Wine - Our Endless Numbered Days). I've determined the his is in the actual recording!
As someone who appreciates honestly hearing the recording, I actually enjoy this, but I was shocked to discover it. I think it has something to do with the mics used, the hiss of the tape or something. It's quite present on Miles Davis recordings or the White Stripes.
To give you an idea of how this changes from track to track on the same record, compare the two songs below. Even with the compression YouTube gives us, the difference is quite start to my ears. (Drive has it, Nightswimming doesn't once the piano cuts in)
R.E.M. - Drive
R.E.M. - Nightswimming