How to guarantee to lower noise- ground loops in your system

If you run a dedicated 12 gauge (or lower) Romex (etc.) to your rig, and use a plastic box, then you already have an " Isolated dedicated ground." You only need an IG if you don’t have a dedicated run. 

Sort of. Technically the dedicated run will be grounded back at the panel, which in turn is grounded to the service ground. Service ground is the copper rod driven into the ground, typically right beside the house and very near the meter. 

Which you probably know.

The OP and all his comments are so infernally confusing even I was just about totally lost. The link he provides is just as bad, not one word on the page saying what exactly they mean by IGR. Had to follow a link to another page where finally it says:

IGRs are bonded directly to the service entrance grounding system.

So there you go. The OP had an electrician install an outlet with a ground wire running all the way back to service ground.

Eliminating ground loops has more to do with product design than electrical wiring, the latter of which should simply be to code.

Actually its neither.  Bottom line is ONE reference - regardless of what that is too (virtual earth, actual dirt, etc.).  Product design can give some tools, but anyone can thwart a designed by connecting several products together (RCAs carry signal ground) and grounding them to subtly different points - e.g.: different outlets.
A dedicated line is good but has nothing to do with loops per se (you cant have a loop with one wire!).  A dedicated ground is good, but you can;t have two (the one the electrician made and the one you run).
Bottom line: back to what i said - everything grounded to one, single potential, in a "shortest path star" config.
And burn incense. :-)
G

Ground loops occur when the resistance between any two or more grounding points is high enough to cause enough of a voltage drop to be detected & amplified.

To reduce this:

1) Attach ALL your devices that handle signal circuits to a STAR configuration, ie to the SAME outlet/plug, with short mains wires. That is your turntable, subwoofer, amp, preamp, DAC, etc. If you do this, make sure you have a 20-30 Amp circuit to be able to carry the load of your megawatt amplifier. The more the better (and more expensive).

AND/OR

2) Use NON COPPER signal connections if you can (optical or fm/radio/wifi).

AND/OR

3) If you must use MULTIPLE outlets/plugs (no other choice), make sure the resistance of the EARTH connection between those 2 (or more plugs) is as close to ZERO ohms (the THICKER/OFC the wire the better) as possible.

If you do one or a combination of these, you will not have a hum problem.

In order to have a Dedicated isolated ground ,a plastic box does not qualify,read the link I included from experts a seperate insulated ground wire connected to the outlets then to the Copper
ground inside the breaker box. Nothing more to be said just ask a 
electrician

Service ground is the copper rod driven into the ground, typically right beside the house and very near the meter.

Nope. The Service Ground is the Powerline transformer neutral. The copper rod is for lightning protection. Many homes do not have a copper rod. They rely on the foundation rebar mesh [Ufer: https://en.wikipedia.org/wiki/Ufer_ground] or tie to the cold water inlet. Multi family building are an entirely different kettle of fish.

The 3rd wire ties in the panel to the Mains transformer Neutral [Center Tap] - the wider terminal. It is the earth safety. NO current flows in the Lightning Earth Safety rod when a fault trips a breaker.

Have a look at the drawing http://ielogical.com/assets/M-125/PTPolarity.jpg . It shows how ground currents can flow from transformer induced currents and poor inter-stage grounding. The lower section shows operation with power transformers in phase and a Loop Breaker installed. See https://sound-au.com/earthing.htm#s9 on Rod Elliot’s "Earthing Your Hi-Fi - Tips, Tricks and Techniques." UNLESS YOU ARE TRAINED AND 200% KNOW WHAT YOU ARE DOING, DO NOT MODIFY YOUR EQUIPMENT. The life you safe may be your own!

"teaching the Tubes4HiFi / VTA M-125 to sing" was an exercise in getting rid of ground loop hum. http://ielogical.com/Audio/VTA_M-125.php/ The amps are 40db quieter than delivered.

Adding a copper rod can make a system unsafe as the potential between the copper rod and the original earth can create a battery and eat away the rod. Acidic soils eat away copper unless there is a sacrificial less noble anode.

Additional rods must be placed based on their length and the effective length of the existing earthing scheme. Placing a rod willy nilly may increase the impedance and reduce the effectiveness of the earth lightning safety connection.

@millercarbon: Please do not pontificate on things that may make a system lethal.