I had the same thing happen on one of my Von Schweikert VR-1 monitors that I bought many years ago on Audiogon. I heard a rattle in one speaker when moving them. I took it to a local repair guy and it was just something loose within the crossover. It was a quick and cheap fix. I still have the speakers and they always sounded great. The fact that it happened to both of your speakers leads me to believe that it is a manufacturing flaw/weakness in construction that was unmasked by the stress of shipping. As mentioned above, upside down position should have zero effect on the innards of a speaker.
Glad they sound good. Enjoy them!