I seem to remember an in-line filter fitted on the S76 position lights at the rear of the tailboom. I'm sure that it was to stop HF interference and any other nasties. The easiest way to prevent HF interference (especially on the AFCS) is to remove the HF form the aircraft.
There are rumours that one particular helicopter has a problem with its FADEC eng computer and mobile phones in the cabin. But I'm sure the manufacturer concerned has sorted all this out by now...