I’ve noticed a problem with hissing through earphones when plugged in to the 3.5mm jack and after a search, I’m not the only one. It seems to be more noticeable on my Shure E4c canal-phones than it does on a pair of first-gen iPod earphones. The volume at anything below 40%, depending on the gain on the track, allows me to hear the hissing but turning the volume up too high will be uncomfortable.
Having had a problem with the lack of bass using the E4cs on an iPod, once solution was to increase resistance by using an attenuator or putting some resistors inline along the wire. Thinking of this, I used the remote that came with the N95 and the bundled earphones but this didn’t do anything. Next, I tried the volume attenuator that came with the Shure E4cs. This allowed me to turn the Music Player volume on the phone, up to over 40% to reduce the hissing and then to reduce the volume again at the attenuator to a comfortable level.
If you have a hissing N95, give this a try!