Whistling sound from PC

[Antithesis]

Regularly when I use my PC, it briefly makes a whistling sound, the same one I hear when it's turning off. The fans keep on running, the performance is good, and it does not shut down. So it does not cause direct issues, but I am afraid that my system will get damaged if I don't address it. This has happened under multiple OSes.

Specs:
Motherboard: GA-H110M-S2H
CPU: Intel i5-6400 (Skylake)
No video card

What causes this problem? Is it safe to ignore it or no?

 

[RememberThe5th]

Do you mean on startup and shutdown?

 

[evongugg]

Wires touching the CPU fan?

 

[Antithesis]

It's the same sound I hear when I shut down my PC, but I hear it mid-use.

There's one wire near the CPU fan that was a bit loose. I repositioned it and will try it like this.

 

[RememberThe5th]

Just to make sure download hdtunepro and check health tab cause hdd can reproduce same noise.

 

[Antithesis]

There are no cables blocking the CPU fan and it still happened once. HDTune Pro says all my components are healthy.

 

[lakimens]

Could be a a faulty fan, hearing it speed up and slow down.