DIAGNOSIS A low-level electronic hiss from the speakers when idle is generally normal for active speakers like the Ray, but it shouldn't be loud enough to hear from your couch. If it's audible from your seating position, something's amplifying the noise floor.
FIX First, check your source and cables. 1) Turn off or mute your TV. If the hiss stops, the issue is likely coming *from* the TV through the optical cable, not the Ray itself. 2) Ensure your optical cable is firmly seated at both ends. A loose or damaged cable can introduce noise. Try a different optical cable if you have one handy—they're cheap and can be the culprit.
IF THAT DIDN'T WORK The noise could be electrical interference from another device sharing the same power outlet or power strip. Unplug everything else from the same outlet/power strip as the Ray (game consoles, chargers, etc.) and see if the hiss reduces. If it does, plug the Ray into a different outlet, ideally on a different circuit.
HEADS UP If the hiss is present even with all inputs disconnected and persists after trying a different outlet, it could be a minor defect in the unit's internal amplifier. If it's very noticeable and bothersome, and you're within the warranty period, contact Sonos support.