1yo house bun, happily shares most of the house with the cat, dp and I. We have a gate across the doorway between kitchen and lounge so he can't chew wires in the lounge, but he can see dp and I. He has access to food, water, litter tray, hay, toys etc.
He occasionally stamps once for no apparent reason. The other day he stamped about 3 times so I went and gave him a cuddle. Tonight he was stamping every 4-5 seconds so I went into the kitchen (his favorite chill out place is there as well as his food) but there's nothing there to scare him 
No one has walked past the house. We're fairly urban so very little wildlife (if he heard a fox or owl for instance). The cat's asleep upstairs and is normally seen either batting balls to him or being chased around the kitchen by him 
I went out to give him a cuddle and some reassurance - he's very affectionate usually - but he hopped off uninterested so I've ruled out attention seeking. He's not stamping now, so has clearly calmed down.
Any suggestions? I don't like thinking he doesn't feel safe 