Static electricity can build up on the pickguard (if the pickguard is not shielded) and cause static scratchy noise, especially when you touch or rub your hand on the pickguard. It also varies from person to person because some people don't generate as much static electricity as others. This problem is most common with Fender Strat guitars but it can happen with any instrument, I suppose.
To see if this is your problem, try rubbing your hand around on the pickguard in the area between your pickups and control knobs. When I did this on my Precision it produced static every time. When I play, I pluck the strings in all different areas, sometimes anchoring my thumb above the pickup and sometimes using my thumb with my fingers anchored on the pickguard under the pickup, so this was very critical for me. Some players that never touch the pickguard may never even notice if their pickguard would produce this static. Different weather conditions can have an effect on this too, as well as what shoes you are wearing and what kind of carpet you are walking on, etc. We're talking about static here, so all these factors can have an effect.
A quick fix for this static cracking problem is to rub the pickguard with a static dryer sheet (like Bounce). But this is only temporary, I've heard that one rubbing may last as long as a couple of days. A permanent fix is to shield the back of the pickguard. To do this, some people apply spray adhesive and then put a layer of heavy-duty aluminum foil on it. When you put the pots back on it makes contact with the foil for a proper ground (the shielding must be connected to ground to be effective).
My preferred method to shield the pickguard is to use a 12"x12" sheet of copper foil with adhesive backing (can be bought at stained glass shops for $4 each).
My CIJ Precision had static scratchiness generated by the unshielded pickguard and I totally eliminated it this way. Using the 12"x12" copper foil sheet, I was able to cover all but about 1.5" of the tip of the lower horn (of the pickguard) with one continuous piece. I then just put another small piece on that tip of the horn, though it wasn't really necessary. I think it may only really be necessary to shield the areas over the control/pickup cavities and wire routes, but I wanted to do the entire pickguard. The static scratchiness and popping which was generated by the unshielded pickguard is totally gone now.
Of course this may not be your problem at all, but it's worth looking into.
