Bunny query!?

I rehomed my friends rabbit yesterday, he is so layed back he may aswell be horizontal! He s happy as he s running around, when he lays down he stretches right out plus he s washing himself in front of us. Happily eating and drinking also. Even playing with the curtains lol. But today I ve made sure I ve been sitting on the floor with him just to get used me to (not pushing my self on him) and while he s been running around he will make a buzzing noise, thump then come straight over to me, have a sniff and run around me, then goes about his buisness again... Was just wandering if anyone knew what this was about. Thanks in advanced :D