If you have a modern face plate, the bottom bit pulls out. In doing so you also take all the other bits of kit out with it so it isolates the input line from the rest of your wiring and appliances. Think it is called an NES 5 socket or something (which you may or may not have). The I Plate is just a way of isolating the 'third' (orange) wire, which isn't needed these days and can unbalance the signal lines and make them more susceptible to noise - but only as induced on the internal wiring. So first thing is to see what the 'raw' signal is like and to see if it differs markedly from what you see normally. If so there is scope to improve your internal wiring.
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