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 ???

Could you be overdriving your speakers? I once hooked my VMPS bookshelfs up to my Krell Ksa-250 and they did the same thing (snapping sound) at high volume levels.

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.