[SOLVED] Why do my h100i v2's fans make that strange sound?

[ProPlayerGR]

Hello everyone. I have a h100i v2 and its fans make a weird sound. It's been happening since the day I bought it, but it only happens in summer because it gets very hot here in Greece and the room temperature is like 30 degrees. Here watch that video and listen the sound:

View: https://youtu.be/mUswf-R32bI

Thanks in advance.

 

[RARRAF]

the fans are noisy I bought some
NOCTUA NF-A14 PWM 140MM PREMIUM PC FAN
no noise

 

[ProPlayerGR]

the fans are noisy I bought some
NOCTUA NF-A14 PWM 140MM PREMIUM PC FAN
no noise

I know they are but what is this strange sound?