Speaker keeps getting muted

When I advance the Microphone volume, it mutes my speakers. Is that wierd or what?

Yes that’s weird.

What sound card do you have?
What’s your operating system?
Which version of Audacity?

Not that weird.

One of our Linux distributions does something similar. You note the level is a little low, so you adjust the volume and Audacity will switch to a different input. Switch back manually and everything’s OK again. In that case, I think it’s an interaction with artsd.