A hiss that is not audible is not a concern. If you can hear hiss it can be both good and bad. Good if your hearing is great that you can pick up the faintest of noise from a low noise, high quality gear. Bad if you know that your hearing is not as good as it was before and you still hear a hiss on your new shiny gear. That tells me I got a lemon. Especially, if I can get another sample of the gear that is hiss free.