Hi there, firstly sorry if this is in the wrong thread. I am a noobie to sound production and equipment. I have just purchased the following:

2x KRK RP5 G3, 1x Focusrite Scarlett Solo. 1x Shure Sm7b. I am getting an issue where my Rokit speakers are making a humming noise with high pitch sounds in and out when they are plugged in and on with all cables connected and no sound chosen to play through my computer. (One speaker has a considerable louder humm but sound playback is not louder, this is the same even if i swap which one is L or R on the cable connections.) The sound is only present when all audio cables are connected. This is much louder when I move my led/laser mouse (Razer Deathadder Elite) and/or I change the brightness of the LEDs on my gaming RG Keyboard (Corsair Strife).

I am connecting my mic to my audio interface with a balanced XLR cable. I am connecting the monitors to my audio interface with a Stagg STC Dual Mono Jack to Phono Cable (3m/10ft, Black) - STC3PCM. Which i believe is a dual phono to 1/4 jack connection which I have been told is unbalanced (apparently all phono connections are unbalanced??)

My PC is a custom gaming build I made about 6 years ago. With 2 internal fans and the graphics card has fans. All the power sources are coming from one extension tower going connected to a wifi range extender with a plug slot coming out of the back which is connected to the mains. I have done a few tests to try and diagnose the issue. I will go through them.

#1 I plugged everything in same way with same power sources to my girlfriends laptop. The monitors worked fine no hum unless my ear is right up to it so I can only assume they is normal. No issues playing music either. (Never had studio monitors before)

#2. Back into my PC. I changed the source for the two power cables going to the monitors to another mains plug on the other side of the room (2m away) No change.

#3 I changed the usb slot connection of the audio interface x4 times. No change.

#4 I unplugged my mouse and keyboard. Slight reduction. Still bad though

#5 I unplugged all usb connections bar the audio interface. No change from above

Once again I am massive newbie so no idea what i'm doing tbh. I have been reading around, potentially earth humm mixed with ime from my mouse/keyboard which enhances the earth humm?

I am planning on returning the focus rite and getting a ID4but I am not sure if this is a good idea as apparently all phono connections are unbalanced and this could be contributing to the issue.

My gut says its a mixture between audio inter and the pc and led/keyboard screwing with it.

I wonder if a power conditioner is recommended if so which one. Also comments on recommending product i.e audio inter/cables would be appreciated as well as just basic explanations of things.

I would really appreciate as much as anyone can give. I am happy to spend money on new interfaces and equipment and try pretty much anything to get this stuff to work. I look forward to your replies and will be looking around the forum to learn more. Sorry once again if I have posted in the wrong place.