I’m currently getting what looks like ground loop humming (low consistent noise) which comes from my left monitor out channel of my SSL SiX plugged into my Genelec 8020s. This is happening when:
- The SSL SiX is turned off, and the Genelecs are turned on.
- The sound disappears when I turn on the SSL SiX.
- There is no unwanted noise coming through the headphone out or any other outs on the SiX.
- I have unplugged all other cables to and from the SiX and this still happens.
- This happens only on the left out channel on the SiX.
- I have tried swopping cables.
- This is not the left Genelec, as it does this also when connected to the right.
All my studio gear is running from the same UK plug socket, and into 3 extension leads. I’m around 420 Watts max, and that would be with everything running, so I’m well within what the socket can handle. I have tried to connect the SSL SiX, and both the Genelecs to the one extension lead, and this still happens.
I have also removed every other plug in the extension lead and I’m still getting the noise.
I wanted to see if anyone had any experience of ground loop noise, and what recommendations do you have to deal with it? What’s good practice for how you handle your electrics? Any recommendations on good extension leads? 
Could this be an issue with the SSL SiX?
I’m know this is a boring AF topic, but any help would be appreciated. It’s driving me mad, day after day (since last Friday)
UPDATE For anyone interested it was my DB25 connection. It’s fixed now.