I had a timing belt fail on an old petrol Cavalier sometime before 2005 (I only know this date because that's when I replaced the car.)
One evening driving home from work, while waiting for traffic, I noticed a very low rate thumping sound - about once per second. The following morning it failed to start, the starter just spinning. I prised open the plastic timing belt cover just enough to see the belt but it looked OK, so I called the AA man. He looked in the same place while I cranked the engine - and could see that the belt was not moving. So he towed it to my local garage where it was repaired. Happily not an interference engine.
Clearly the belt had frayed and the thumping sound was part of it clouting the housing as it went round.
By contrast my sister had a diesel VW Passat estate, belt and idler replaced by local garage (near Glasgow) at the specified service. She drives to Colchester to stay with our mother. Almost on arrival - bang!
- and engine stops. Garage in Colchester investigate - belt has failed. They suggest it was incompetently fitted, in that the idler was not tightened properly so had worked loose. Wrote report, which sister took to original garage. They protested their innocence and tried to claim that the VW part was badly manufactured. Eventually they paid her some small compensation (probably the materials cost of the replacement belt and idler). So she was seriously out of pocket with the cost of the work done by the garage in Colchester!
Even more annoying - she was working part-time for the Glasgow garage as their book-keeper - so you would have thought they would have treated her better.
Which leads to the old adage - the best way to ensure a piece of machinery does not fail is not to let a maintenance technician anywhere near it!