Some iPhone 7 users are reporting that their phones are creating a whining sound from the back of the phone when the phone is performing some sort of stressful activity. One of the first reports was from Twitter user Stephen Hackett, who also provided a video that demonstrated the whine quite clearly, coming from the back of his iPhone 7. As per the user, the sound was loud enough to be heard with the phone sitting on the desk, and it was recorded while the phone was syncing with iCloud. Several other iPhone 7 users also reported that they too were hearing whining of varying...
Source: http://www.gsmarena.com/some_iphone_7_users_reporting_coil_whine_issues-news-20573.php