pjw1967

Went out yday and after a few minutes of driving my seatbelt did what I guess was a safety retraction. It pulled me back against the seat and then released. Scared the crap out of me. I was going about 15 mph approaching an intersection. There were steel plates covering a trench but I don't think the front wheels had reached them when the belt retracted. About 10 mins later I was siting in a parking lot with the car idling in Park. I felt what seemed like a shove and the car rocked once front to back. No wind at the time. Any thoughts? Thanks.