I remember we got stuck there one night, coming back from Belle Vue. There was a loud knocking sound coming from the floor of the coach, and nobody could find out what it was. The driver didn't want to take any chances, so we spent several hours, waiting for a replacement coach.
We discovered what it was the next day...
Someone has nicked a metal road sign for a lark. Not thinking, they stuck it face down under one of the seats. It was dark, and the back was the same colour as the floor. When we hit bumps in the road, the bloody thing would knock against the frame of the seat ..