strange new behaviour from bunny

I have two bunnies (male brothers) who are now 2 years old that we've had since they first left their mother. They are both neutered and are happy together. They are comfortable in their cage which is of a large size giving them room to run around and stretch comfortabley on two levels. They are allowed to come out and roam at their will around the room in the evenings and get supervised time in the garden when weather allows.

Both are used to human contact and while they don't like being picked up they will usually get stroked happily. One bunny (Crothchet) is more 'tame' and attentive than the other (Quaver). Quaver has always been the more dominant of the two. He has always been the more investigative and cheeky of the two, digging a lot in corners, very skippy and very active when running around the room. Crotchet wanders happily, skipping when he feels but at a more mellow pace.

In recent weeks, both have tended to remain in their cage, not venturing very far except on the odd day. There has been no change to the room leading up to this change. Quaver has become a lot more jumpy. He jumps away from human contact and has on occasions pounced at mine and my partners hand while we're stroking Crotchet, something he never did before. I am concerned at the sudden change in behaviour as they both used to be so curious and nosey.

There have been no changes to their diet and both are eating and drinking as normal.

Any advice would be much appreciated.

I don't think them retreating and not coming out so much is a huge concern becaise its the time of year they might bed down and if both are doing it thats an indication its behavioural as opposed to physical.

The behaviour that would convern me would be Quaver's and why he is acting differently. Have there been any additions to your home? Has he had a vet check recently?

There have no new additions and no visitors in the time since his new behaviour began. The only thing we can think of is new people moved in upstairs and there is a young child who jumps around a fair bit. However they've been exposed to noise before as there was work being done on the house over the summer and they didn't seem bothered by that all.