RF intererence can come from:
halogen light source
wireless router in the room
active cell phone (or old cell phone)
any other high output light source
high output electrical wires (lol unlikely)
But most likely, due to the proximity to the TV and the TV speakers, that's prolly it.
and like what technokid says, is it really a hiss? shhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh or
bbbbmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
or
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee (lol)
<--- audio n000b..but i'm an EE major, so i'm not entirely n00bish, but still n00b