Here are two links to some additional reading material on the subject. Seems from a bona fide source. Personally I split my system load between two GFCI devices and do not use a grounding probe. For added redundancy, each GFCI is on a different circuit breaker. The only buzz I have ever experienced is while brushing my clip on T5HO reflectors with my arm while my hand was in the water. I assume the T5 lamps induced voltage in the reflectors and I completed the path to the water through my arm. I have since individually grounded each of my reflectors and the problem is solved. This was not sufficient to trip a GFCI device, so I also assume the buzz was harmless, below the danger threshold of a healthy individual. Someone with a pacemaker might have had a problem. If I recall correctly, before grounding the reflectors, I read about 30 volts AC between the reflectors and the water. So that potential was always there, but had no place to go until my arm completed the path to the water. If you install a grounding probe in your system, the same situation
may arise, with a voltage potential with no path, until a grounding probe or you provides it.
http://angel-strike.com/aquarium/GFI...alDetails.html
http://angel-strike.com/aquarium/GroundingProbes.html