Some iPhone users have reported hearing a hissing sound when they overwork their new iPhone. This is indeed a very odd issue compared with the previous bendgate (my iphone 6 plus not easy to bend lo).
According to an article from 9to5Mac, iPhone 7 users reported hearing "hissing" sounds from their phones when the latest A10 processor were under heavy load. This was first noticed by Stephen Hackett of 512 Pixels and subsequently corroborated by other Apple users. Hackett uploaded a 6 second video as above with a recording of the hissing sound which sounded a bit like the white noise from your tv sets. Hackett checked with AppleCare support and was told to head to the nearest Apple Store for an exchange. The Apple store he visited did not have any spare stocks and it would take 5 working days for a replacement unit to arrive. It has certainly raised some concerns from the general mobile phone users but this is something minor compared to Samsung's exploding phone phenomenal. But not many users have reported this issue as of yet, so let's wait and see and i am sure i will test it out when i get my hands on my own iPhone 7 Plus.