How to get rid of a gray scrolly thing???

Hello! I'm very new to Premier Pro. I was listening to some of the stock audio and this gray highlighted scrolling box showed up in my timeline when the audio was playing. When I finished listening to the audio, though, it didn't go away. I have no idea what it's called, so any attempts at looking up how to get rid of it did nothing. Help please! And thank you 🙂