I have had three rats in my life, all of them the sweetest things. After the loss of my last one, It took me a long time to make the decision to get another. I got Penelope 6 months ago. She is a fancy rat. She is very friendly and outgoing. She has tons of energy and loves to use me as a playground. She is completely normal when she is on me, she can sit on my shoulder all day. However, if I'm sitting down and she is free to roam around the couch, she starts to act very bizarre. She runs around like crazy (will never stop moving), twitches, hops in the air for no reason, and bites me. She doesn't act like this when she is in her cage, or when I'm carrying her and walking around. Has anyone every had this happen with their rat, or have any ideas to what causes her to act like that?

Strange. I've never had a rat but a few people who frequent the board do so we'll see what they say. When she bites, is it play biting (doesn't hurt much) or serious biting (draws blood or really hurts)? Since she's an intact female, it may be related to her hormones and perhaps some frustration in that department. The running and jumping sounds normal for a young animal having fun. When my cat gets excited, he sometimes bites me too but he's happy and doesn't mean it; that's play biting. I hope that's what you had.

Howzit, Sorry that I'm replying so late :( , but when I joined I was only interested in goldfish. ;)
I've bred and kept just about any form and species of rodent I can think of, I might not know the scientific names of the creatures or identify all the subspecies, but I do have a lot of experience in this field. :)
I wouldn't worry to much about your rat, I've had similar experiences with my rats.
First of rats are super, i repeat absolutely incredibly inteligent creatures, so never underestimate their ability to have feelings.
In this case what immediatly comes to mind is the familiarity( in other words safety ) of her environment, when she is in her cage she is safe, when she is with you she is safe( BTW I get the impression that you give her loads of attention, which is brilliant, many people get rats and forget that they need more than physical care, they need love, attention, intelectual stimulation, and it would appear that you take great care of her.)
Try to allow her to get used to specific environments, e.g. you usualy sit on the couch, so allow her to explore the couch, get to know the couch and know that it is a safe area, an area that INCLUDES YOU!!
Take into consideration that rats are naturally hunted by an immense number of predators, as such she will be nervous when in a new environment, she'll just have to grow up, and learn that you are not a predator. :lol:

Also she might be having a maybe allergic reaction to the couch, it may be senthetic, or the couch cleaner or maybe your boyfriends' deoderant :lol: , I have had some of the strangest things recieve some of the strangest reactions from my rats, they may be hardy surviving little buggers, but they are still intelligent and sensitive creatures.

I wouldn't worry to much, your rat sounds to be in perfect health.
I've had these similar eratic reactions before.
If you are still worried, maybe your vet can check her out, she may just be paranoid, super sensitive and as such never adapt to other environments than you and her cage, no problem, just makes her a rat that is even more loving than they usualy is. :P
B)