I just bought the M8 yesterday and noticed a very strange problem with the phone audio. Whenever I play music or make a call, there is a screeching noise that appears every 5-10 seconds. I tried upgrading to 4.4.3 as the phone was on 4.4 when I bought it and still the problem remains. This problem also appears when I put on the headset. The sound would just go crazy and screeching then just go completely silent. I haven't installed any apps yet on this phone so I don't think there are any rogue apps that cause this. Also tried resetting the phone but didn't work. Has anyone else experienced this problem?