This has nothing to do with the volume control! I have this hiss with every other application too! The audio path from the M11produces audible hiss with high sensitive headphones. On my Beyerdynamic DT1770 i hear nothing over the 3.5 jack. With my ibasso IT04 on the 2.5 jack i hear this hiss...

This is "normal" with high sensitive Inear. Some DAP have hiss problems with high sensitive earphones! :-(