Count me among those who own and love the SoundSticks II. No hissing from mine either. You might have a noisy power line, a cable TV input, or some other electrical problem. Try a power line conditioner or test the SS-IIs in a different outlet in another room.
I am surprised by just how good the SS-IIs sound. Much better than any Altec Lansing, Creative, Polk, or other computer speaker I've auditioned. There may well be better units out there, but the SS-IIs are just worth every penny to me.