Keypad tone during call

[AC Question]

Hi. So today I was calling my friend when all of a sudden, I hear a keypad tone like as if someone was pressing on the keypad. I asked my friend if she hears the keypad tone as well but she doesn't hear it. I'm the only one that could hear it. During the call, I would heard the keypad tone like every minute or just randomly. It's never happened before. What do you think is the problem? Is it a glitch or is someone tapping the call? I wasn't using wifi calling during the call. The phone I have is the Samsung Galaxy Avant and I have T-Mobile on it.