Yeah, one of our girls does that, too. Rats make happy noises that are usually too high pitched for humans to hear. It seems that some rats have a "deeper voice" and we can actually hear the little "beeps" they make while investigating. It's adorable, really.

 

Hmmm...rats are normally silent, could it be her breathing you are hearing instead? Little squeaks could mean a possible URI flaring up.

 

Ill try to get a video, so I can show you guys.

 

I have a super mouthy rat, you do have to be carefull if this is a new thing for your rat. It could be a sign of a URI and they can get out of control really quickly. My rat makes all kind of noises, he's got to be the loudest rat in the history of rats and he makes happy squeek noises... actually his sound alot like a parakeet.