Furman solves ground loop issue?

It solves the salesman's problem of how to keep his job.

I hope your interconnect cables are well shielded and designed for phono signal, not just regular interconnects. Also i hope your tonearm is grounded, you can try additional wire with stripped ends (one to you phono ground input, another stripped end to your tonearm metal part) to check if the hum is gone or not.  

I had a vicious ground loop in a system that used a residential cable modem with an incoming coaxial connection. The cable modem was connected to the same circuit as my home theater preamp and self powered speakers. I tried disconnecting one signal cable at a time in the system until I isolated it to the coaxial cable entering the apartment. So I drove to Fry’s, bought a coaxial grounding block and ran a ground wire from the block to the ground on a wall outlet. Boom, ground loop was silenced. It turns out that cable tv/internet companies love to run coax signals extremely hot to prevent loss, especially in apartment and condo complexes.

Later, a different system with a headphone amplifier connected to a DAC with a pair of XLR cables in a balanced differential setup was getting horrendous ground hum. It only occurred when either of the two (or both) was connected to power AND to each other via the balanced connection, right channel, left channel or both. Neither hummed on its own. On the advice of an old school audio repairman who was factory authorized by brands like Luxman, McIntosh, Mark Levinson, etc, I snapped both ground pins off the (removable) power cables. Hum gone instantly. (I don’t recommend this unless you know what you’re doing and what the source of your hum is. Another option would be to put a very nice isolation transformer inline in the signal path; breaking the XLR ground.)

As you can see, hum can come from many different kinds of ground faults in a complex audio setup!

engineears

... a different system with a headphone amplifier connected to a DAC with a pair of XLR cables in a balanced differential setup was getting horrendous ground hum ... I snapped both ground pins off the (removable) power cables. Hum gone instantly. (I don’t recommend this unless you know what you’re doing and what the source of your hum is ...

I don’t recommend eliminating safety grounds under any circumstance - that’s treating the symptom rather than the disease. It can be useful as a diagnostic tool to isolate the source of a ground loop, but it’s not a solution to the problem.

NEVER remove the ground pin. Use an adapter if you must lift a ground. It is best to check first if the ground pin is connected to any of the signal leads. If it's chassis only, removing it will have no effect.

Is it hum or ground loop? They are not the same thing.
Hum will usually be a purer tone than a ground loop which often contains buzzy noise components. Triac dimmers are notoriously noisy and phono cartridges make excellent pickups.

Have you checked the ground integrity. Many buildings have essentially no ground. It can be due to poor design, corroded connections and silly electrical code like allowing bonding to rebar in a foundation aka UFER. My HiFi is connected to a copper rod that goes 10 feet into the ground. It has a dedicated circuit.

How is the gear arranged? Please list components and positions. Sometimes just re-arranging power cords or component position will solve the problem. Power cords should never be coiled or bundled with audio leads. Power cords should only be as long as necessary and cross audio lines at right angles.

Sometimes gear has a resistor between earth and its zero volts. Sometimes adding a ground lead from the offending gear to the next can solve the problem.

Be sure everything is off when changing connections.

Noise elimination is a step by step process. Start with the power amp alone and shorted inputs. At the absolute worst, there should only be a slight hiss with ear right next to drivers. If there is any hum, there could be something amiss with the amp or more likely the wiring. Add each preceding component with it's inputs shorted. Noise should remain nearly constant. If it increases, there is a system / wiring fault which must be corrected.

Assuming everything up to turntable passes, use shorting plugs on the phono input. If the noise is gone, the problem is the turntable / cartridge. If not, disconnect the phono AUDIO and apply shorting plugs

If the turntable is the problem, reconnect audio and disconnect the cartridge. Short the cartridge leads. If the noise is gone, there is a problem with the cartridge / phono input. Is the type / impedance correct?

If you must connect CATV - why?- to a HiFi, use a balun to isolate it, if necessary.

Using optical connections wherever possible on digital audio will preclude any possibility of ground issues.