what does it mean when a rat clatters it's teeth?

I have two young male rats. I got them a week ago but I went on vacation so my neighbor looked after them. When i first got them they were really shy, now they're not afraid of my hands anymore. One of them is really shy and hides all the time, the other comes out to sniff at me. To get them used to me I let them get into their little house and put it on my desk while I work, or I put on a big pullover and let them sleep in the pockets/hood. Yestreday I had one of them climb around me for two minutes maybe before hiding in the hood again (for their standards it really is a lot). Later when I took the pullover off to put them back in the cage the less shy one (which was to one who had climbed around on me) was sitting in the hood so I stated gently stroking it with one finger. It put its head down ad started quietly bumping its teeth together quickly. Does this mean it liked me stroking it or was I intimidating it?