Noise coming from PSU only under low CPU usage

I had to rebuild my PC getting a new MOBO/CPU/RAM, but PSU and GPU are the same as before. I'm having two issues, not sure if related. One is that there is an annoying noise coming from my PSU. I believe it's similar to this one and it's the same PSU (Corsair CX 750) https://www.youtube.com/watch?v=dvyZWz9iYkQ

Two important details: I've been using this PSU ever since my old MOBO/CPU/RAM and I haven't noticed this noise before, so it's new. The second detail is that this noise only happens under LOW load. If I use 100% of CPU (rendering video or stress testing) the noise simply disappears. I start stress test, it's gone. I stop it's here again. The PSU is new (I bought it on December 2017).

My second issue is that I'm getting mouse lag (I've never had this issue before) when there is an external HD connected. I don't know if it's related to my PSU noise because it doesn't change it. I believe I don't have mouse lag while not connecting an external HD or it's much better without it. I tested other wireless mouse and it has the same issue, haven't tested a wired mouse.

My specs:

CPU: AMD Ryzen 5 1400

RAM: 8 GB Corsair DDR4

MOBO: Gigabyte AX370

PSU: Corsair CX 750

Wireless Mouse: Logitech M280

Edit: As suggested by u/nukefudge I disabled Global C-States on my BIOS and the noise is gone. I'm not 100% sure the other issue (mouse lag) is solved, but if it's not I'll start a new thread focusing on this.