I have seen this before.
When you leave your car anywhere it is always a good idea to stay close by.
I have friends who have left their car for work who came back to pick it up and for some reason the rear end now has a terrible hum to it.
Turns out the guys in the shop made a few pass up and down the road just to check out their new work they had done.
I saw one guy who went to look at his New back halfed chopped 39 coupe and he pegged the guy at the shop to let him just take it for a little ride down this country road.
This tried to talk him out of it but they could not so they told him to make sure he took it easy with those new big back tires going around any corners.
We watched him take off and then roll the car three times when he got to the corner.
He was sitting there crying when we pulled up!!!!!!!!!!!
True story. Jimbo