https://m.youtube.com/watch?v=xalTFH5ht-k&t=99

This matches my memory of 56k dialup with the two BONGs.

And now I get to share my favorite AT command. M0 could mute the modem! M1 was quieter than the default. I will never understand why those weren't more common! Used like: ATM0DT

I never wanted to mute, because with sound you could hear a bad connection early and retry faster.