Noise suppression and the yellow wire

[Eliosso]

I have a noise problem on my ''boat theater system ''. I have an LCD screen and DVD  and installed a FM modulator the send the sound to my stereo system.. When used dockside on 110 , everything works great. When at anchor, using the inverter , Xantex 1000, TV and DVD work great but when I activate the FM modulator, I get a strong hisssss from the stereo so I end up not using the modulator, not that's it's a big deal but would like to solve the hissssssing. Any ideas would be welcomed.
Paul