Sir Percival,
Although it will not help you, rest assured you are not alone. It's usually the gearbox cross member that catches humps, bumps and other things.
I have banged mine so many times that, apart from periodic checks underneath, I have given up worrying about it.
If I see a hump coming and it looks bad, the Memsahib gets out whilst I approach it very slowly. She is a hero !!
