Hello,
I started using the N800 for MP3 and the hissing sound was driving me crazy. I turned off the touchscreen click and now everything sound great. I normally use a set of noise-reduction headset for music and for some reason if I leave the noise-reduction turned off, I do not get the hissing but if I turn the noise-reduction on, I get really loud hissing.

Anyhow, thanks for the suggestion on how to fix hissing.

Denny