To be honest, my instinct is to say "yeah, and maybe you can pick up russian spies with your dental fillings." IE - poppycock.
However, it is possible that some combination of corded attachments and internal circuitry leads to the formation of a filtered antenna which is then amplified to the speakers. In theory, this shouldn't happen if the devices are functioning as designed, but some degrading of components or manufacturing defects could potentially contribute to such a scenario.
Consider how some speakers will buzz and chirp if your phone is near them. Similar idea, just that it would be with aircraft radios.
It could also be that they are driving into radio bands not regularly used due to higher traffic, or something, or using ones not technically supposed to be used under FCC guidelines because they are afforded for device noise or some silly thing. Been a while since I studied all of that in any kind of detail.