iPhone 8 Plus Sound Distortion

I am using an iPhone 8 Plus on iOS 11.0. I noticed that when I am playing song on loudspeaker, there are some kind of "noise" or "distortion" to the song, every time I make some actions that would trigger sound feedback, e.g. typing on the keyboard. This will also occur when I browse in the App Store while listening to song, especially when the App Store video tries to play automatically. This issue does not happen while I use a headphone instead. Apparently this issue also exists in other iPhone 8 and 8 Plus. Is this hardware defect?