That'll be caused by eustachian tube dysfunction, the question being what is causing said dysfunction.
Do you suffer any allergies? If there is a seasonal pattern to your issue it's fairly suspicious for an allergic exposure of some kind.
NZtechfreak,
It
is fairly suspicious in this way, and in point of fact, the treatment has been for me to take Claritin--an alergy medicine--and that usually works, although sometimes I need to do the Claritin D thing. So yeah. The thing is that when it happens it's usually hard to mistake or miss--in the past there's been no doubt about it--whereas right now, if it's happening, it's pretty mild relative to past episodes.
However, the other thing that makes me suspect this is that I've been doing A/B testing for the last 30 minutes between the 5S and my Apogee Duet, both driving my Grado SR225's, and I've been
sitting up, whereas before I was lying down to listen. And I'm not experiencing the listening fatigue--so far.
More importantly, I'm pretty impressed by how well the iPhone 5S is doing in this A/B test! As I said before, I like the sound I've been hearing straight out of the headphone jack. This is the way I always listened to music on my iPhone 4.
I hear it as more aggressive than the 4S which I don't remember sounding very different than my previous 4. That could cause fatigue.
The 5S
is more aggressive than the 4--no question--but what I am (was?) experiencing couldn't really be explained by this, I don't think. More like high intensity 19kHz noise spikes or other sorts of hard to pin down distortions. But I'm not
hearing any distortions, though! In fact, I fired up my Signal Generator app and listened to a straight sine wave output, sweeping up and down the frequency range, and all seemed as it should be.
I'm hoping that this all has nothing to do with the phone, and everything to do with me and a seasonal allergy. Because most of what I use my iPhone for is listening to music, and if that is going to be pain inducing, then obviously I need to return my 5S and figure something else out.