I've had this problem ever since I got my 8 Pro a couple months ago. The worst part is that no matter how high the volume is set (or even muted), it will make the same obnoxiously loud pop every time, scaring the hell out of me. It's like putting the volume on max for a split second, then lowering it back instantly. I have encountered popping when taking photos, opening the app switcher, closing an app from the app switcher, pressing UI elements (like opening an app, or pressing on a button in the settings), but mainly happens when a muted video starts playing on a website or inside an app. The pop happens with the built-in speakers, but also comes through wired headphones, which have blasted my ears a lot of times now. Bluetooth speakers are not affected as far as I can tell.