Oh, nostalgia. I had a US Robotics 56K modem, which produced two bell-alike sounds during handshake. It was cool. I search for that specific sounds for years and cannot find.
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
Last time I asked, user hackmiester pointed me to https://goughlui.com/2016/05/03/project-the-definitive-colle...
The "Texas Instruments DSP based Modems" linking to USR-Sportster-bong-bong.wav is pretty close to what I remember.
edit: hackernudes reply is perfect. The youtube auto generated subtitles are pleasing too.
Comments: YUP.