FaceTime static noise when opening apps on iPhone

Hi, this doesn’t happen frequently, but sometimes when I’m on a FaceTime call, and I go to open an app, for example safari. My FaceTime call just starts making this static noise/buzzing sound and I can’t hear my friend and my friend can’t hear me. How do I resolve this without hanging up and calling back? What is the best way to resolve this without the call hanging up?

[Re-Titled by Moderator]

Original Title: why when im on facetime and i open an app sometimes it makes this weird buzzing sound or radio static noise?