I have an Octavia mk3 2015 with the 1.2 liter petrol engine, and it has recently started making some strange noises.
I suspected it had something to do with the AC system since the noise stops when I shut it off, but i also noticed that when the noise is happening and AC running the internal light also flicker very slighlty, which made me think the problem might be with the alternator, its pulley or the belt.
I've attached a video, if anyone has expirenced this and can give me some info that would be very appreciated :)

Not something I've heard myself, but sounds like there's something mechanical trying to kick in but not entirely successfully.

I'd start at the easy bit, check the battery and charging are ok with AC off. Then measure voltage with it on, and see if there's a correlation between the noise and a voltage drop.

Get your AC operation checked over anyway, as you don't want anything seizing and causing further problems. A good mechanic may well just listen and know what is amiss.