Even if an aircraft passes its EMC testing, as far as I'm aware, that testing is conducted on a 'fresh-out-of-the-hangar' aircraft. Whereas in-service wear-and-tear can cause other issues....
I recall flying a rogue VC10K whose rudder pedals would tremble and CCTV screen would flare whenever a transmission (or even 'blip tuning') was made on HF/SSB. Basically a leaking antenna feeder cable induced transients into the yaw damper system (and, with autopilot engaged, the rudder pedals) - the CCTV flare was equally obvious as being proportional to transmitted audio level (and hence SSB RF modulation level).
Boscombe published frequency restrictions for certain phases of flight for the VC10K; however, most aircrew just ignored them or accepted that "There might be a bit of intereference" with which they would cope....
I agree with tucumseh; the Board's comment is far too glib regarding the potential of RFI from unknown on-board transmitting PEDs causing UCMs.