What's snapping?

I have been getting this "snapping" sound through all speakers from time to time and last night it was driving me crazy. It was happening every couple of minutes. It sounds like a static charge releasing itself, if that makes any sence. It does it on all sources. Right now I am using a Harmon Kardon AVR7200 as a preamp for a Mcintosh MC352. It was doing it before the Mcintosh arrived so that can be ruled out. I think it must be the HK or the Monster 2100 powerbar. Is it possible it could be a bad cable or dirty connection even though it happens on all sources?
I am finding it difficult to narrow down because it doesn't do it all the time. Today the system has been on for almost 2 hours and it is fine.
Any ideas ???

You dont say if your using a power conditioner or not. It could be that you have something on your incomming voltage line like a switching power supply. Make a note of when it happens most and try to narrow the environment, time, weather, traffic if in a apartment, and perhaps whats happening around your area, like what is on in the house, what are you using that might tap into the electrical.

It might sound like alot but I traced a snap down to a lighting fixture that had a bad ballast.
Thanks so far guys, I sure hope it's not equipment related. The Monster power bar is a stage 2 power conditioner.
Now that I think about it, it does seem to happen mostly at night. It is strange because both my wife and I swear we've only heard it on movies, until last nights hockey game. All along I figured it was the DVD player.
I'm not worried about any damage occuring, so I will have to live with the sporatic annoyance. That is a great idea Dlstephenson, you've given me a couple of ideas I must further investigate.

I'll keep you posted.
It's not static if it happens with all sources (about 80% sure on that one) and not cabling (I agree w/ Porziob) then I'd guess RFI -- probably not a faulty ballast however (although could be, but that's not the kind of RFI they produce.)

I'd guess some kind of device with an arcing relay, like a fridge or airconditioner compressor, or an electonic ignition device like found in a gas water heater, furnace, or stove, IMO.
I suggest removing the Monster power bar from the system temporarily to eliminate it from the list of suspects if that's possible.