Simaudio MOON 610LP with Lyra Kleos

So..a new issue? Can you be more specific as to when you first noticed this issue?

It is a new issue. But each one of these components have been used in other combinations, including cables. 

Just an idea, I had a hum problem with my center channel and mono amp for driving it. I inserted a Jensen Iso-Max isolation transformer in the interconnect, and 90% of the noise went away. It might be something to try. I have a two-channel analog set up (using the same main speakers, separate tube preamp and SET 300B amp) with no noise issues.

Hope you get it sorted out.
Regards,

Dan

With a step up transformer, you will take a significant hit in sound quality.

I suggest that you check Bob's devices web site for his article on grounding problems and how to solve them. It is the best piece I have seen on the subject. You probably don't need a step up transformer with a .5mv cartridge but I can tell you from experience with many cartridges that a good step up transformer helps
the sound stage significantly on low input MC cartridges. 

Finally, I would bet that you have a ground loop hum somewhere in the system. Make certain that all of your phono cables are far away form electrical components with transformers.