Sam's Club is as evil as Walmart, so it's probably some kind of cosmic payback!

But seriously... is this a bike with vertical dropouts? If so, you could have ridden the whole way with the QR not tight enough; and if it's not tight enough, it will vibrate loose(r). If your bike has horizontal dropouts, you cannot ride it unless the QR is really tight.

My verdict: if you have horizontal dropouts, someone must have messed with your bike. If you have vertical dropouts, there are more possibilities than we can really evaluate here...