IPhone 5 voice call quality fade in and out. Noise Cancellation interference?

Question

I've been having this huge problem with the iPhone5. The evidence i've collected seems to indicate this is a problem with all iPhone5's.
On calls in certain places both indoors and outdoors, the callers voices over the iPhone5 fade in and out. Their voices occasionally completely fade completely away, and only come back momentarily. The low volume for 50% of the time forces me to raise the volume, but raising the volume does not help because when the voice does come back, the volume is too loud for my ears.
I went back to the Apple store and they are not able to help me. They suggested a clean restore, which I did. They offered to replace the phone, which I did, but it is the same problem.
- iPhone 5 vs. iPhone 4S, the fading does not occur. I make the call to the same voice mail system I have, and the sounds from the other side are consistently the same volume for the 4S, but fades in and out for the 5.
- I connected up a 8mm jack between my iPhone 5 and my mac in an attempt to record this problem. In that instance, the sounds from the voice mail DO NOT fade in and out. I did find out that the dynamic range on the iPhone 5 is MUCH greater than that of the iPhone 4S, for some strange reason.
- When I hold the phone up to my ear, the fading in and out does occur, but it is less noticeable. But it's still there.
- When I leave my work area the problem goes away. However, because the iPhone 4S on the same AT&T service does not have this problem, this leads me to believe it's NOT a lack of transmission power from the AT&T cell tower. Rather, it is a reception issue at the iPhone5 side.
- I turned off LTE, data and then made the calls. Same issue.
I use this phone to make 60 minute calls for conference calls frequently. I cannot use it. Please advise. I am seriously considering returning this phone. Except i've sold my old iPhone 4 already. I'm in a bad place. Please help.
Here's another post of a fellow with the same exact problem.
http://forums.macrumors.com/showthread.php?t=1456404
Apple, please look into this. I believe this is a problem with the noise cancellation software.

Answer 1

I've got an update on this problem with fading volume. I've isolated it to the set volume on the phone for voice calls when using headphones. When the headphone volume is set between 1 and 6 (out of 16 squares) the callers volume will consistently fade in and out. The fading which is normal to zero volume at 2-5 Hz is serious enough that normal conversation is impossible.  When the volume is raised above 6/16 then the callers voice stabilize and I can hear all their words again. Unfortunately, at 6/16 volume their voices are too loud for the headphones.
Furthermore, when headphones are plugged in, and I initial a call after the iphone5 was idle for several minutes, the first dial tone has preceded by a very loud pop an the tone, as though there was too much pressure (charge) that was dissipated all at once.
Other details:
- I used 3 different earphones, iPhone 4 headphones, altec earphones, an the new iPhone 5 earbuds. Same.
- I turned on and off lte, data, Bluetooth, wifi. Problem persists unaffected.
- when switching to iPhones earpiece and mic, the fading is gone.
- I have 3 out of 5 bars where I teste this, in the city outside and on hwy 5 in central California. Same symptoms in all places I've tested.
- I have exchanged my phone at the apple store. Same issue with both iPhones an I suspect all ipjone5s.
- the ipjone4s does NOT have this problem when the volume is set lower. I can tell that the iPhone 5 must have a new audio filter to make the sounds have larger dynamic range. I liked the 4s better, because it is easier on the ears!