The main reason for thumping is to alert others of danger and to express anger. Some are more “vocal” in their displeasure than others. Some will thump at every little sound, needing to alert everyone of danger. Like Chacha said – some thump for attention. Sort of a “hey! PAY attention to ME!”
I’ve never read this as being an actual behavior for thumping, but Eddie used to start racing around, thumping whenever he would get REALLY excited about something. Coincidentally, it was usually when I’d give some banana. LOL He was also good at startling himself awake and freaking out, thumping while he dashed for cover. I knew he was startling himself because I would look to Lolli to see if she was scared too and 9 times out of 10, she was perfectly fine and looking at him like the dumb boy he was sometimes. lol
I wouldn’t worry too much about your bunny thumping unless he seems scared and is trying to dash for cover all the time. Then you might need to do some investigating. I would always look at my bunnies to see why they were thumping but as long as they weren’t both scared, I didn’t pay too much attention. Otherwise he might just be more “vocal” about everything that honks him off – good AND bad. LOL