bend the phone? lol ok. and the fact your 7 plus came like that and you had to tighten the screws is awful all around. None of my 6+, 6S+, or 7+ did this.
Yeah, the same way you're applying pressure to opposite corners of the phone in your video. That's not exhibiting regular use.
Just have the Genius Bar tighten those two screws, and it should no longer make that sound.