It is mostly a hiss.  it appears to be coming from the tweeters of both speakers.

I don't have this if the speaker are paired with my BeoSound Moment. (i need the Transmitters so I can use my non B&O TV via the receiver)

They supposed to make a 'white-noise' hiss.

As you stated that the hiss is not there withthe moment; some recievers are not grounded properly. Is the reciever connected to sat/cable device through hdmi or cable on it's own? 

the hiss continues when the music is playing and is audible.  there is no hiss at all when they are wirelessly connected to the BeoSound Moment.

It isn't the receiver, because if i unplug the receiver from the BeoLab Transmitter, the hiss continues.  If i unplug the Transmitter the hiss stops (as the speakers are no longer paired with anything.)

The speakers always have a 'healthy' white noise hiss. As the moment swnd digital audio straigh from source it could also send 'gain' and 'mute' like signals. As the transmitter always has to open the gain becouse of the analogue input the 'healthy' hiss remains. It's hard to test this theorie. Maybe gain settings are needed? 

they are connected wirelessly.  and there is absolutely no noise when the play from the moment.  only when they are paired with the transmitter is the hiss there.

As i said, the transmitter converts analog-in to digital. The transmitter sends a uninterupted singal to the BL with high gain. The moment can 'pause' broadcast / between songs and noise is masked. Touch the phono connectors while the transmitter is broadcasting; noise.

The transmitter gransmit with gain setup too high.

ok.  yes, touching the phono plugs or the phono cable increases the hiss.  so i need to determine how to reduce the gain on the transmitter, probably with a command on a the usb stick?  (i do hear the hiss with music as well when it is playing).