I propose if Card was indeed wearing high powered hearing aids it is highly plausible he was being intentionally targeted with some form of Electronic Warfare (possibly microwave radiation in the 1 to 2 GHz range) or some form of Psychotronic Weapon utilizing V2K (Voice to Skull) Technology.
Lastly, I have to mention the most recent Netsux Predictive Programming Obama Globo-Homo production of Leave the World Behind.
A Microwave Psychotronic Weapon is used in the movie several times.
Each time there is a ear splitting sound where ALL of the cast are effected but only one (the teenage boy) shows physical symptoms (ie his teeth falling out).