I don't recall hearing hiss when I call my voicemail and leave a message on my old phone which didn't have visual voicemail. This morning I activated with visual voicemail set up and called and left messages. I hear a loud hiss the whole time but it doesn't get recorded with the message. I was thinking of switching to basic and trying again. I don't see how it can be the S7 itself, maybe samsung has their own servers/equipment that generates a hiss?