Dell OptiPlex 7070 external speaker humming with Realtek audio driver

The external speaker on my Dell OptiPlex 7070 SFF starts humming every few minutes. A quiet low level, deep hum. Sounds a little like the speaker is vibrating on the desk. You can clear it by playing some audio or clicking the volume control button to make it ping. This is happening on Windows 11.

The installed driver is the latest one from Dell using the Command Update software. Its listed as version 6.0.9235.1 (7 Sept 2021). The problem goes away again if you revert to the Microsoft driver "High Definition Audio Device" version 10.0.22000.1 dated 5 June 2021.

To install it right-click on the Windows menu, choose Device Manger then Sound, video and game controllers. Right-click Realtek Audio > Update Driver > Browse My Computer for drivers > L
et me pick from a list and choose the High Definition Audio Device. You can accept the warning about compatibility.