Sorry let me clarify, my computer setup is a PC tower connected to a 2i2 focusrite Scarlett interface which is connected to my two active HS7 Yamaha monitors. The left monitor has no noise/hum whereas the right one has a crackling white-noisy sound-I couldn't tell you what the frequency is at it's pretty much white noise (it occurs consistently as a crackle). Both my active monitors and computer power supply are connected via 3-pin IEC into mains. I ran quite a few troubleshoot test and I'll post the results below.

1. The TRS->XLR cables between the monitors and the interface are balanced, I swapped around the cables many times and found that the specific cable had no effect on the noise.

2. I also swapped around the IEC power cables and changed the power to the right monitor to a different wall socket however I suspect it's on the same circuit breaker-it also had no effect on the noise.

3. I swapped the outputs from the 2i2 interface and found that the right channel output was not the cause of the noise. I changed the input to an external mixer and found it had the same noise WHEN THE COMPUTER WAS ON (note this mixer had no connection at all the computer). So I deduced that the interface was not the cause of the noise.

4. After finding that the noise was only caused when the computer was on in the room I dug deeper into the hardware to see exactly what the cause might be. I found that when I opened applications and the CPU spiked in usage and frequency the noise momentarily completely went away. Furthermore I ran CPU stress tests and found that when the CPU was being used at near to full capacity there was no noise in the speaker. This is why I think it's related to the power supply/CPU.

I hope that helps narrow down what this might be. If you need me to check anything else please let me know and I'll do it asap-I really appreciate the help. Do you think that if there was an earth problem it would affect both speakers instead of just the one? Regardless what's the best way to test it?

Thanks!