New Dedicated Line - Almost No improvement

I used 1/2 or 5/8 solid copper pipe (not an iron/copper grounding rod., 6 feet long. We drilled straight down, hammered the rod in and then filled the hole with a high-clay content soil.

Is the grounding electrode only 6 ft deep in the earth? If so unless it rains a lot and soil moisture content is high you have a poor high resistance ground, imo...

I hope this is not the only earth connection for your electrical service. The System Ground, Grounding Electrode System, is mainly for lightning protection. It also somewhat protects the electrical service from a high voltage fault of the high voltage power line onto the low voltage secondary side of the power transformer from entering your house. The lower the resistance of the Grounding Electrode System the better. IEEE recommends 5 ohms or less.

Example of grounding electrode depths in the earth. (Climate Change and droughts would make things worse)

http://www.cpccorp.com/deep.htm

https://droughtmonitor.unl.edu/

A practical guide to earth resistance testing

I used the 25 ft long/deep iron drill pipe for my water well.

I would guess you have a good low resistance grounding electrode. I wouldn't be be surprised if it measures 5 ohms or less.

A practical guide to earth resistance testing

B

Be aware that large isolation transformers hum.  I got rid of mine for that reason alone - could not keep it in the listening room.  I understand that they may not be so objectionable if based on a toroid, but that those have other limitations.

@lloydc My BPT 3.5 Sig., a toroid only hummed when I had over voltage (122-125v), built c core bucking transformer to cure the over voltage, no excessive hum. Since upgrades by electric provider, now provides 119-121v 24/7 no hum from  transformers in any of my equipment.