[WPCentral Question]

I got a Lumia 925 back in April and it's worked fine and got 8.1 preview when it came out. A month or two ago my ear speaker slowly started fading out/crackling during a phone call and the sound never came back until I did a complete factory reset (still on 8.1). It's happened again; reverting to 8.0, then going back to 8.1 and another full reset didn't fix it. I'm on tmobile prepaid and both times it happened when I was trying to call with a terrible connection and only a couple minutes left on my account, but I don't know if that's related. Also, it would start fading out and stuff during one call but the sound would be fine during the next call for a bit and then finally go away completely. Speakerphone works fine. No damage or anything to the device.

Is this the fault of 8.1 or is it hardware or T-mobile or what?

Thanks