Did you try a simple cheater plug on the Sutherland power cord. I know that that you did try a Hum X but that is not as simple as a cheater. I used one succesfully on a CDP which also introduced a 'buzz'.
Help! Can't Get Rid Of Buzz in system at Higher Volumes
Help! I currently have a VPI Prime Scout TT with a Nagaoka MP-500 Cartridge loaded running through a Sutherland Insight stage/preamp into a Marantz SR7012 AV Receiver. With the turntable input selected on the Marantz, when I turn the volume to around 50 or above without playing a record, I am hearing an annoying buzz that I am unable to get rid of. This is not a 60Hz hum but more like a 120Hz buzz. I've tried using a Furman power conditioner strip, a HumX from EBTech ground isolator, using two different power outlets for different components, different phono cables, a variety of turntable-to-stage ground wires, etc. The noise is not present when using other Marantz inputs. The only thing I haven't tried is installing a coaxial isolating transformer for the coax cable coming from my DirectTV satellite dish (I doubt if this is the problem as I don't notice the noise when the TV Audio Input is selected) and disconnecting a dimmer switch (on the same wall as the A/C outlets that power my audio system) that controls a resessed light over my fireplace mantle. Any suggestions as to what else to try? Thanks much.