XS1930-10 - electronics noise

Hi Zyxel Support and community,

I am evaluating XS1930-10 and this device is quite unique and meets most my needs except one area ... noise. I can accept noise level when fan spins around minimal RPM (3500), but my problem starts when temperature raises. I have noticed then strange clicking / rattling sound. It occurs only above minimal RPM and clicking frequency changes with speed. Firstly, I was thinking that it was caused by rattling fan bearings, but no. When I am manually forcing fan to stop, clicking still exists - source of it is from electronics or PSU. This is weird and unexpected behavior. My question is - is this normal?

Why this is important for me? I have plan to replace internal fan with Noctua ones. They are dead silent, and I can put more than one to provide enough airflow with less RPM. But this is pointless idea if something in electronic circuit can be so loud...