UncleBob, I have been having this exact same problem and, like you, it has only been recent (last couple of months). I am on my second launch 3DS. Nintendo shipped me a replacement after the first one mysteriously bricked after about 8 months.
I have always suspected they shipped me a refurbished one anyway.
My system gets jostled a fair amount as I carry it every day either in my coat pocket or in my backpack. But I have not dropped it. It is supposed to get moved around, though, right? All that counting of steps and whatnot?