Kathy, Do your hearing aids have a telecoil on them? If so, you might find it helpful to use a neckloop or direct audio input cord (a cord that brings sound directly into your hearing aids -- one end of the cord has shoes/boots that snap onto the bottom of a behind the ear hearing aid -- the other end plugs into the device you're listening to). The telecoil might block out enough of the hissing sound if it is used with a neckloop, direct audio input cord or even headphones.
By the way, I'm glad you mentioned the hissing sound. I received a cochlear implant in December and am now learning how to use my BrailleNote with speech. When I used my BrailleNote for the first time, I kept hearing what sounded like a hissing sound, but I couldn't tell if it was coming from the BN or my CI. Lisa
