I did not experience this, my grandpa did. He would not make something up like this and not tell me it was made up.
Anyway, he does drywall for a living. One day he was at a house putting drywall up when he had to use the bathroom. So, he went to the bathroom, and then returned to his work. About a minute later, he heard the toilet flush again. He knew that no one was there with him, and that the doors to outside were locked. He went into the bathroom and looked into the toilet. Sure enough, the water was swirling around. Puzzled, he checked room and found no one. The window was shut and locked. He searched the whole downstairs and found all the doors and windows locked, and no one there. To make sure, he also checked the upstairs and found the same results. He went back into the bathroom and made sure no one was there. Then he heard, "He he he!" He ran out of the house and went home.
The next day he returned with a co-worker and finished the job. Afterwards, my grandpa told the other guy about it and he said, "Why didn't you tell me in the first place? I wouldn't have come!"