Just curious but when you say no load does that mean no assumed load i.e. with all appliances turned off or are they actually tripping when no current is measured flowing through them?
I hope it's not the first signs of the Earth's magnetic field reversing

Apparently it happens every x no. of thousand years and we'll be utterly screwed when it does it again!
Hmm... another thought enters the mind. It appears it's a quite a good one too. It's almost as good as Danger's suggestion about being between two magnetic fields (which I'd suggest to the power company), so here goes:
I wonder if it might be possible that part of your building is not connected to earth. This is entirely possible if the installation electrician was not too clued up and what should go where to put it as politely as possible, especially given that you've had to fix several ground faults of his.
So is it possible that two large parts of your building which are made of metal and say running parallel to each other are being charged up by the nearby power lines. Over time they will act like a large capacitor if they are both isolated from each other and ground.
Perhaps your events are being caused by things occasionally making contact with them and causing them to discharge like perhaps your 'glowing wire' palletiser for example.
It would explain large stationary magnetic fields in your premises which have been wiping data on hard drives. It would also explain large discarges through your earthing.
It would also explain why your phones don't work, and why sometimes the current being discharged is huge like in the 'glowing wire' palletiser example.
Might even explain why your breakers are tripping with no load. Depends how big the static field is.
I'd get your voltmeter out and test your building's metal structure's voltage relative to ground. In fact try and find a piece that is isolated from ground, then have it's voltage with respect to ground montiored constantly for a few weeks and see how it changes when 'events' occur.
Have a look for walls or roof panels which are large and are situated opposite each other. It's a suggestion which comes mighty close to an explanation of everything that's been going on. Also explains why they don't happen all the time and why some are worse than others, it all depending upon how long they are being charged up by the power lines before something links them together and they discharge.