I have a mouse that makes that sound. He only does it when he's all in a twitter about something.
The first time he did it, I thought it was a URI and even isolated him and treated "it" for 10 days. I never heard the sound during the 10 days, but about 15 minutes after I put him back with his women, he started it up again. After a lot of tub swapping, I found out he had some objection to one particular girl and that's what he was babbling on about.
I don't know what emotion is behind it, but he also does it when babies are born in a tub with him. He gets so wound up, I can hear him making that noise from the next room! Sometimes I wonder if he's trying to tell me the babies are his, or if he's trying to deny all responsibility.. :lol: