Portable devices

[carbheathot]

This question is purely academic(I'm a humble ppl with an a level in physics) what is it with mobile electronic devices such as i-pods or perhaps portable dvd players that can affect the Aircrafts electronics?
I can see the problem with mobile phones when being used to transmit calls etc, but don't understand the portable appliances issue

[Intruder]

Possible RF interference when both the device and the airplane have improperly shielded wiring. Remember that even "non-transmitting" devices give off RF energy that may escape the boxes if improperly shielded.

I have seen reports in the past of problems in specific small commuter-type airplanes. Whether it was because of inherent design defects or maintenance problems, I don't know...