squeaking rats

Question
QUESTION: My sister has four pet rats.  When she is petting / rubbing them, they squeak.  It is definitely a squeak, and they only do it when she's rubbing / petting them. At first I thought they may not like it, but they close their eyes and press their heads into her hand when she's doing it. They never make any attempt to get away, as they do with my niece, or to try and bite to indicate this is hurting.  It's the first time I've heard rats squeak, other than from fear. Does it sound like they are squeaking because they like this?

ANSWER: I have never heard a rat squeak from being content either....I would love to witness this.

---------- FOLLOW-UP ----------

QUESTION: Thank you.  Would you agree, from the description, that they seem to be squeaking from contentment, rather than discomfort?  I tried to describe it as accurately as I could.

Answer
If they were unhappy, they would run away and would hide and not allow her to continue petting them if this was the case.

I have heard a rat whimper from fear before...it was heart wrenching.  My rat, Santana, is terrified of cats and has never really been around one before, but when he hears them meow outside the door he freaks.  One day he was by the door and the cat was on the other side and was trying to put his paw under the door. This scared Santana so bad he went flying back to his cage,and he was up hiding in his house whimpering like a little child. It was so sad!  I have never had another rat that did that nor heard other rats do that either.   Anything is possible with these guys thats for sure!