I have just bought the Zgemma H.S and have connected it to an RF modulator via the Red, Yellow, White A/V cable, when I put it on the main TV it is connected to via HDMI it is fine but when I try it on other TVs in the house the picture is there but the sound is not, it is just a constant hissing sound that you would get on a channel that has nothing on it, can anyone help, also, the picture fits perfect on the main TV set at 16/9 but not on the other TVs set at 16/9. Thanks