Might of been just the brakes. They might have a little rust to wear off on the inside of the drum. Sure stops quick when there is no wieght on the tires don't they? Doesn't hurt it any that I know of but wouldn't want to drive it "60" and go nowhere.

The sound might, I say might, be a wheel bearing also. That's how I always double checked a rear wheel bearing is jack it up and run it, you can hear them a lot more.
When it's time to come out of hibernation, check the oil in the rear, brakes and wheel bearings. Good thing to check all fluid levels anyway.
And Chooch could be right on also as there is sure a difference between on the ground and not.
Deb