iPhone 6, purchased in Nov 2015. During voice calls the other end is experiencing really bad distortion or interference. What happens is I can hear at very low volume what sounds like GSM interference. The kind you get and goes; da da dada dada da da da da da da (older audio equipment or guitar amps often pick up the sound. Nokia even used the phenomenon Innone to advert)..... Once I hear this I know the person on the other end is possibly hearing the same but at a dramatically higher volume or plain distortion of my voice. To the point calls end as its impossible to continue. Sometimes it distorted for the other end without hearing this sound also . I also have another iPhone 6 purchased a few months later. This does not suffer the same interference problem. If I need to continue the call I use this in the same environment and location and the call is perfect every time. The phone is under warranty and also extra apple care and I will revert to this. However I wondered had anyone experienced the same problem? To my mind it's as if some hardware or software shielding has failed.