More Electrical System Madness

So, after getting the new subpanel, dedicated lines, hubbell receptacles, fiddling with grounding arrangements, etc., system is dead quiet (remember, it is a horn-based system, about 104db efficiency, so I'm hearing alot of stuff I wouldn't have heard on my old electrostatic set up).

What is disturbing me is a nasty 'snap' that goes thru the system periodically, sounds like a ground disconnect/connect at gain (or a monster scratch on a record at full volume, but that ain't it). At first, I thought that the Air Line arm compressor was surging when it kicked on, even though that is powered thru a separate wiring set up than the hi-fi. (It was plugged into the regular circuit in the room, not the dedicated circuits). So, I had another dedicated line, etc. hooked up, terminating at a different subpanel, to run the compressor. Now when the compressor kicks on, the room lights no longer dim, and no compressor power 'surge' is heard. But, there is still this periodic electrical 'snap ' through the system, and I don't think it coincides with the compressor activity. I rechecked all my equipment grounds, tight and true, don't think it is a bad tube (is it?) and otherwise am clueless as to the origin of the problem. I thought the dedicated lines would eliminate any interference from appliances in the house. Assuming that's true, then the problem either originates from the power company, or the dedicated electrical system in my house, or one or another pieces of equipment.
You hear this snap when a record is playing, and to be sure, if you cue the arm up, but keep the gain up, it will periodically snap thru the system. I haven't timed it to see if it occurs at precise intervals yet.
Any ideas on cause, or approach to solving this?
I had a central air conditioning system with electrostatic filter system (with faulty ground) that did exactly what you describe. Of course it could also be a random static charge going through your turntable and/or phono, or even your refrigerator or other appliances going on and off.

Unfortunately what you describe is the symptom and the cure can be difficult to find.

One question. Do you know if your electrician put all your stereo gear on the same "phase" from your breaker box?
yep. Considerable discussion of that, and other issues relating to the installation of the "dedicated" system, in another thread relating to its set-up. I went back through all the grounds after I wrote the initial post, decided to pull the Granite Audio grounding wires from everything- since I ultimately had to float the Audiopax amps anyway to achieve system quietude, generally- and think I found a possible intermittant connection between the tonearm and the phono pre.
I haven't had a chance to hang out listening to make sure, but I was planning on doing some serious listening (well, maybe debugging, given the problem), so I'll report back.

Thanks for the thoughts, Albert.
Any surge suppressors or power conditioners in your system?
Else, tube problem is not impossible. Good Luck!
Well, it wasn't the ground between the arm and phono pre- so, for my next trick, I decided it still had to do with the compressor for the Air Line arm. Having had that plugged into a separate circuit didn't make a difference, and having a dedicated line for it, run with first class stuff to a separate subpanel didn't make a difference, so, in a fit of pique, I whipped out ye olde extension cord and powered it from the 240v- 120v step-down transformer that I use for the HT system.
That might have done it- I'm going back up to listen to music.
I just have to keep reminding myself that this is a 'hobby.'
Only Shunyata Hydras, but not all of my components run thru them- for example, the Lamm line stage plugs directly into the wall, as does the power supply for the TT. I suppose I could plug those components into a Hydra as well....