Question about inside unit noise

Hey everyone,

Bought a new house in the Netherlands which has two inside units in the bedrooms both coupled to an outside group.

One of the units makes a buzzing noise at regular intervals. the noise will kick in a few minutes after switching it in, and continue even after stopping the system. the other one doesn’t make that noise at all. After stopping the unit, the intervals between the noises will increase until it finally stops.

I looked in this group and generally the diagnostic is a dead capacitor, but all posts I’ve seen are showing a noise on the outside unit, not inside.

Can anyone help me know what the next steps are here? TY!

In the attached video you can hear the noise twice. I opened the unit to try and hear exactly where the noise comes from.