Battery health and buzzing noise

[Reach-Orange-CN]

ROG Zephyrus G16 GU605MV, have been using for 5 months

1. I've been using my computer with the power connected all the time, but once I used it on battery, and it had about 40% charge left. The next day, when I restarted the computer, the battery health dropped from 100% to 96.5%. I am wondering if the bettery health can be recovered or it is just the problem of display.
2. My computer makes a faint buzzing noise that can be heard when I put my ear close to the keyboard surface. I can't remember if this issue was present before or did it only start occurring after I updated the BIOS?

[seerge]

@Reach-Orange-CN

1. Windows / system constantly recalibrates battery health, this is a very approximate measurement. It can go up and down.
2. It's called "coil whine"

[Reach-Orange-CN]

thank you so much!