I got an iPhone 6s Plus about a week ago after previously using an iPhone 6 Plus for about a year. I have continuously been hearing crackle sounds from both speakers when at full volume. I have read around and many people are experiencing this and getting replacement iPhones, but the problem still exists.. Even after the fourth or fifth exchange. Does anyone have any knowledge that this could possibly be a software problem? I heard it has been present since iOS 8.3.