It's funny how I never ever heard hissing on any of my computers... This must truly be a sound card oddity. I'll have to say that the acoustics of some S&M season 1 voices sound a bit hollow/"small room" like, but that improved over time anyway.
About compression: I'm a person who's more annoyed by the compression/low res on textures and stuff sometimes. I'd love for Telltale to lower the compression a bit on these for DVD versions and stuff...