jtveg

I thought it was suspicious when one part of the ad said it had a 1.3Ghz quad core while the rest of the ad said it had a Helio P70 Octa-core.

Believe me it's a thing. Rare but real.

It may also be external interference or poor grounding / earthing. Try plugging the laptop with its charger in a power outlet in another room. If there is a significant difference see what else is plugged in closeby. That may be causing interference.

It may be the laptop's power supply. Does it still make the noise if the laptop is running on its batteries, without the adapter / charger plugged in?