Dell Inspiron 15 7567 gaming tickling when plugged in

Hi everyone!

I have a Dell Inspiron 15 7567 gaming laptop, and today I noticed, that my laptop makes very quiet ticking sound when it is plugged in. This is strange, because the sound very similar to a HDD's head movement ticking. The only problem that there's no winchester in this laptop, only SSD-s (1 X M.2 NVMe PCI-E x4, and 1 X SATA3 2,5") working in my laptop. In this series there's no optical drive, so the only mechanical units in this laptop the 2 cooling fans. But strangely the ticking is exactly can be heard, when the fans stop. So when the fans don't spin (0 rpm) the quiet ticking sound can be heard.

The second strange thing, if I unplug the laptop from AC, the ticking slows down. After i plug in it again, the ticking continues faster...

Do somebody sensed the same? The ticking comes from under the keyboard, if I lean forward, I can hear it well. I think, that this ticking might caused by one electical unit, and I worry that my laptop will go wrong, although now there's no other problem, just the sound...