from my experience,
se535ltd, very noticeable hiss,
ie80, slightly weaker hiss,
denon d600, 25 ohms, when no music playing, noticeable hiss at 2 to 4 o clock
hd 650, no hiss
i think it is the more sensitive headphone that make hiss audible. Plz share with what headphones do you hear hiss, thx!