I hear a slight buzzing noise in my earbuds connected to my laptop.

The buzz is relatively quiet, so I don’t notice it when audio is playing, but it is constant (its volume doesn’t fluctuate, it doesn’t randomly stop and start). No buzzing when earbuds are not plugged in, but it could be that I just don’t hear it over other noise (fans mainly). The laptop is 4 years old and I only just noticed the buzzing within the last week, but there is some (albeit small) chance I somehow just didn’t notice before. The buzzing goes away when the laptop isn’t plugged in (and is running only on battery). Perhaps the weirdest part, the buzzing also goes away, when I touch the metal body (including the back of the screen) of the laptop (even just very lightly, no pressing required) – touching or even pressing the plastic parts (keyboard, touchpad, front of the screen) does nothing. I do not feel anything physically though. Turning volume off also does nothing.

The earbuds are connected using 3.5 mm headphone jack and do not have a microphone. I have not tried other earbuds as I don’t have any other headphone jack ones on me. I have observed this issue in two locations ca. 50 km apart, so that should rule out electricity issues within a building. The power plug does have a grounding pin. The laptop seems to be in pretty good condition otherwise, although it did suffer slight body damage (very lightly bent metal in one corner) when I accidentally dropped a bag containing it from ca. 1 meter height about 4 months ago (I haven’t noticed any other damage, but I can’t rule out internal damage that just hasn’t clearly revealed itself yet).

Anyone here has any idea what it could be? Is it safe to continue using the laptop (any risk of electrocution, etc.)? Are any critical components of the laptop dying perhaps?