If this was already mentioned on this thread, I apologize for the repeat. I noticed a lot of whine noise on the latest CM4 Bookworm image for Devterm with full battery and charger still connected and I vaguely remembered a fix for the stock image years ago…
It was this from @yatli:
There’s a bunch of other stuff in the same repo that might be useful, but I suspect most of the other issues are taken care of by the image itself (like the printer, fan, seems to work already, etc.) Also, I think most of the other things are for A04 and A06, but the battery/charging whine fix seems to work on CM4 as well, unless I’m imagining things. 
Anyhow, it’s a quick and easy build, and install, and it’s just another service to start up to run behind the scenes and tone down the whine. Not sure if it should be included in the Bookworm build, but thought it might be useful to share here in case anyone else was frustrated with the noise.
(Based on other posts to the forum, the whine noise isn’t an indication that’s something is wrong and going to break. But even if it’s not causing damage that doesn’t make it any less annoying.)