I tried it briefly with UHA6S, but did not notice any distracting amount of hiss. Let me try it with other sources and update this post in the night.
@Ritvik,
What are the sources you have tried them with?
Clip+, Cowon X9, Sony E353, Arrow 3G, UHA6S: No Hiss
iPod Video 5.5G: Yes, there is hiss