House Rabbits new Habit

Question
We have a house trained neutered male bunny and he has begun thumping his back feet continually.  There is no danger around no dogs etc.  Why would he have started this behavior?

Answer
Rabbits thump for a variety of reasons.  Most often it is the warning sound when startled or frightened.  

Sometimes, it's to get attention.  Sometimes, they do it to announce their presence.  Some of mine have done it at the start of a run, particularly if my presence indicates it's time to go back in the cage.  Sometimes, they're protesting your actions, or lack of action if you're late with dinner.  Sometimes, even neutered males will do it to indicate their happiness with you.  

Without more info, it's difficult to determine what may be causing it.  If something has triggered the fear response, you may have to try to calm down his area where he thumps the most.  Try shutting out some of the outside sensations with a sheet around the cage, or shutting the door to the room his cage is in.