Isolated Ground causes ground hum.

@JEA48

As far as I know, the NEC does not specificity a maximum number of ground rods, so long as they are all bonded together. That's what I am referring to.

Best,
E

@ erik_squires

Thank you for the clarification.

Yes you are correct there is no limit to the number of earth ground rods as long as they are all tied together. They then become one electrode. One ground wire is extended and then connected to the service entrance neutral conductor in the main electrical service equipment/panel.
Jim

Check out the Ground Master box from Puritan Audio. It will cost you $165 you will just need to connect your ground wire to it. You can read Paul Rikby’s review.

Please don’t add any ground rods yourself. 
Have a licensed sparky do it. I’m sure it won’t improve your current sq situation. 

Don't understand why you would want to add ground.
If you live in the USA your household 120V power has a ground wire for protection from isolation failures as to make the breaker pop.
The neutral is connected the center-tap on the 240V transformer on the pole outside your house. 
The neutral carreies only current when a load is connected and will have a voltage potential to the ground in the outlet equal to the resistance dropout from the load current. 
This protection scheme can sometime cause trouble, and is one of the reasons balanced audio is used to explicitly avoid ground loops.
Leakage currents in high voltage transformers can also be a problem, and may leak into other windings on the same transformer.
You could try an ultraisolation transformer to isolate your neutral from the house neutral/ground.
I have 2000va Topaz transformer for this.
Adding ground rods nilly willy is not a good idea.