I have a microphone, but keep voice chat turned off in game, always. If I use voice chat, it's through discord with people I know. I do not like talking to random people in game.
Today I was in a party, and the person I was with asked, in text, why I wasn't responding to them. I was confused because they hadn't said anything. I was having a conversation with someone in the room, and they told me exactly what I was talking about. They heard every word and thought I was speaking to them. I had no voice chat icon on. Voice chat was turned off in game. I could not hear them. There was no indication the game was picking up my microphone at all.
The situation was super creepy. I don't know what caused it, I don't know if it's repeatable, and I have no way to tell if it's happening unless someone tells me they hear me speaking. The microphone icon that shows up when voice chat was not there, there was none...zero...indication voice chat was on whatsoever, and it didn't broadcast any voice from the other end. Very, very unsettling.