buzzzzz, where did i go wrong?

JD, you can try to measure the resistance between the various grounds. You can go from the ground on the breaker box to each individual rod and see what resistance that you get. If you get readings that are all very close, that is a good thing. The further apart the readings are, the more potential for hum and ground loops. This will also verify that you have a good connection from the box to each individual rod.

Another test is to measure from one ground rod to another ground rod. This will measure the conductivity of the soil around each individual rod. Obviously, the lower the reading, the more conductive the Earth. It is possible to have rods located within just a few feet of each other and have VERY different levels of conductivity. I recently did some digging around my house and found that i had a very high clay content in one section. Moving over just a few feet showed very little to no clay. Obviously, this would make a BIG difference in terms of conductivity and ground potential. Sean
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Although I am armed and with a multimeter I am rather one the level of one who has just enough knowledge to get himself in trouble. So, in order to check resistance, do I simply turn the meter to the ohm symbol and touch the rods with the red and black probes?
DOes the power have to be off to those circuits? Since teh rids are quite a bit distant from each other I assume I can attach jumpers of copper wire to the rods and touch those.
I actually today tried to check teh resistance at the outlet level by putting the red and the black into the common and the ground hole on the outlet. I was not sure if the power should have been on or off to the outlet but I got a number less than one.
It also turns out they use in California something called harmonic transmission which I may have to investigate.
jd

JD, i would first try isolating the conduit from the audio system as you mentioned. If that does not solve the problem ( which i think it might ), then let's take it from there. Having ground rods spaced out quite a distance lends itself to different levels of ground conductivity as mentioned above. One would have to work on either equalizing the ground potential or tying them together so that they share a common path in order to minimize any differences. Sean
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Tomorrow I will install plastic spacers at the mounting bracket of the FIM's to the metal receptacle. Then I will attach the supplemental grounds to the grounding bar at the main service panel. Thanks to both Mar00 and Sean for their help in the continuing great struggle in which I am engaged...someday they will write a book on this...Jerry and the ground loop....maybe some dr. suesslike illustrations

No one has touched on this yet. So try this: 1st hook up the amp to the speakers ONLY. Do not hook the preamp to it. Is hum still present? If so, the amp has a noisy transformer. If not, connect the pre to the amp but dont hook anything else to the pre. Got noise? Proceed on in this way to find out what component is actually causing the ground loop if there is in fact one. I have had a similar problem and found that there was no ground loop at all...I would try this trick before you go any further with the grounding to find nothing is "wrong".