Don't assume that all commercial blu-ray discs are noise free - because they aren't. I remember being horrified at the noise in some of the opening scenes of James Bond Casino Royale - outside the offices where he goes to make his 'second' kill. Noise! Noise! Noise!
So, may be some is being added by the TV (I have one Samsung TV in particular that is worse than others) or maybe it's in your source footage and not being displayed by the computer / monitor. Without some samples it's going to be pretty hard for me to tell
