Could be my source, could be me cranking them too much, but I've heard sssssssssssssssssibilance. It diminishes significantly if I lower the volume. I'm using the same sources for my other headphones, except for using the rear RCA outs for the Koss, vs. the headphone jack for the others, and do not hear the same sssss from my other headphones, even when I crank them. Maybe they are just hiding the flaws in the material better, or maybe the Koss just need more break-in time. In any case, they are very nice cans, with some design advantages (portability being one) that make me like them even more.