Yes, This is unusual and should be checked out. Assuming your house outlet is ok, check your cord and then TT for leakage to ground. I had this happen to me about ten years ago, in my case it was a pinched wire going to the AC that had broken insulation.
Assuming your house current is okay is not a particularly good start. You can get simple little testers
at places like Home Depot that will verify that. I recommend you get one. Once that's verified then proceed with mjl2022's
In answer to your question, it is not usual and it is
dangerous. It suggests current leakage which, though not very harmful at this stage, could become lethal. The shock/tingle your wife and son feel, and the fact that you do not could be simply the type of shoes you have on and just how moist your skin is. I wouldn't recommend you try it, but if you were barefoot and the ground wet I suspect you would feel it...a lot!