Finally ponied up and bought a high end headphone in the AKG K702 65th Anniversary Edition. From the moment I first listened to them, I was amazed at the sound stage and clarity of mids and highs, however, on some of my songs I noticed a "scratching" sound when there wasn't much going on in the music (ie just drums, guitar etc). I was running the K702s naked through my Macbook Air and thought it was simply the sub-par amp/dac that comes with the MBA. I ended up buying a Schiit Stack (Vali/Modi) and while the headphones do sound better with a bit of power and high quality DAC, I can still hear the scratching.
TL;DR I have a scratching in my K702s despite having an Amp/DAC combo and don't know whats causing it. The tracks that I can hear the most scratching are surprisingly 320 kbps.
Any help is appreciated!