Interference On Sound

[Dudley]

I have two Sky boxes, one an HD box which is a recent upgrade in the main room and the other which is about ten years old which serves as the Multiroom box. The HD box works fine as did the old Multiroom box (in the spare room) until just lately when the Multiroom TV has developed interference on sound on all channels. It is not the tv as I have swapped this over with the same result so I suspect the older Sky box may be coming to the end is its life. Has anyone else experienced this or have an ideas as to how this could be rectified? Is it likely to be the Sky box or something else? Not sure which category to put this in. Help please.