This sounds like a classic stray voltage problem.  Somewhere in your system, maybe in every panel box, the white and grounds are joined. And somewhere in your barn or entire electrical system there is a piece of equipment such as a fan or cooler/compressor with a motor problem.

Your recent electricians may have been very safety oriented on the new work they did but the problem is likely in your entire older system.

The code now at least here in WI is that white and green/grounds are kept separate all the way back to the incoming utility meter.

If you take the cover off of one of your electrical panels in the barn you will likely see the white and grounds bonded together. To solve the problem that needs to be changed and may be a big job. There is also a piece of equipment somewhere back feeding voltage through the white wire to the ground wire...which went to your extension cord box and through the drill to ground. You must be insulated enough with shoes etc so it doesn't go through you. A non-conductive box on your cord will eliminate the sparking but not solve the basic problem which will likely surface elsewhere.

This is what causes voltage on dairy waterers and stray voltage problems which cause cows to stop drinking water.