They were singing Tek It by Cafuné. They didn't noticed you for a moment and continued singing. Treble Clef was the first to notice you.

TC: "안녕하세요! 저는 트레블 클레프예요!" (Hello! I'm Treble Clef!) She says in a happy tone.

BC: "안녕하세요. 저는 베이스 클레프입니다." (Hey. I'm Bass Clef.)They say in a calm and mellow tone.