Many years ago, I was finally cleared to go spinning in one of HM's mighty Chipmunks. Take-off, potter up to height, do the HASELLs, then into my first ever solo spin.... Incipient, then into the fully developed phase....
....all of a sudden, there was an almighty crashing and banging from behind. I recovered promptly, found nothing amiss, but decided to return anway.
It turned out to be the loosely knotted ends of the rear seat harness banging against the seat pan, having not quite been fully secured.
Not quite as bad as some chap in an old racing car which had an auxiliary tank strapped into the redundant passenger seat. In the dark, whilst belting down the back straight, the driver felt something suddenly brush his face..
Yes, one of the straps had come adrift - as he found half a trembling lap later when he made it to the pits with his hair standing on end!