Headphones shocked my ears all the time
There seems to be a build up of static energy discharging between the metal frame of the driver and the ear. It's painful and, just like rlaskey said, there's no way to predict when it's going to happen.
And in case anyone's wondering, wearing Nike+ shoes on the treadmill causes the earbuds to shock my ears every few seconds. Running with Puma Lift shoes on produces no shock at all. Go figure.
I have some bluetooth headsets on my Christmas wishlist. If I get a pair, I'm returning my Apple In-Ear Headphones; if not, I'll give Pair #5 a shot.
* Static discharge
I, unfortunately, was seeing *both* issues, which is why I was having trouble determining the cause. I'm scheduling another appointment for later this week (I didn't have the units with me) to return them once and for all. Not sure what to replace them with, though.