How to isolate a gound loop

I am having trouble with a suspected ground loop hum when EAR 868 is on phono. All other positions are dead quiet. Using Bobsdevices SUT. VPI Aries TT. EAR 890 amp. Removed all other devices from system. Tried cheater plugs. Unplugged and removed sub speaker cables. Eliminated Audience LC. Have a dedicated line. Two VPI wands with mono/stereo carts give same hum. Hum is evident without music playing. It's present with SDS off/ unplugged.

If I disconnect the R or L phono RCA to the SUT the hum goes away. With RCA's in and I remove the Lenco attachment, no hum but a static like sound is present.

Hum is present with only the Aroes, Amp, Preamp connected via Audience XLR's, speakers and subs connected via Audience. SUT is connected to preamp with Bobsdevices IC's. TT to SUT via VPI phono cables.

Help is appreciated.
Can you borrow a different SUT? Or since ground loops are not gain-dependent, try running the 'table output directly to the phono input. I wonder, tho, if a very low level ground loop involving the table or its cabling might not be audible unless it is "stepped up" by the SUT.
Looks like your phono pre has either an internal SUT or active gain stage w sufficient gain to allow you to use it w/o an SUT. Total line stage and phono stage gain can be adjusted up to 97 db which means that there is no need to use an external SUT. I would return it and reset the phono stage to a more appropriate gain level, taking into account the 17 db gain provided by the line stage.
Swampwalker, thank you for your reply. I'm not that technical, so should I just play around with different settings or is there one to choose based upon the specs of my cartridge? I have a Cardas Ruby 3 MC.