I sometimes play ball outside with Jack and Tallulah by hitting the ball with a tennis racquet. That way it goes way farther.
I took Tess out, who was happy and wagging her tail and grabbed the racquet. She ran back to the house, tail tucked between her legs, cowering at the door. I put it down, and she came back, still fearful. We did some heelwork, around and right over the racquet, and she was fine. As soon as I picked it up, she ran cowering back to the door.
I got her to take a treat off it, to test how afraid she was, but she only took one off, and then wouldn't touch anymore if I was holding it.
I know sometimes dogs get fears without being beaten, like brooms, but this seems a pretty bizarre thing to be afraid of for no reason. Especially since they were not the tennis playing kind of owners.
Who knows. Yet another thing to desensitize.
The good news is that we are having our roof replaced, so there are guys pounding on the roof and cutting lumber and such. She is laying at my husband's feet, sleeping. So her reactiveness is WAY better than it was when we got her.