I've had 7 guinea pigs. This is normal, especially in babies. Look up popcorning.
I have 13 guinea pigs & they will always be a little jumpy when you first put your hand in the cage but settle down quickly once they know who you are. If they are by themself in the cage & just jumping around a lot for no apparent reason then usually its a new enviorment, something new in the cage or they are scared of something. Their eyesight is very poor so they rely on their hearing a lot. Is there any loud or high pitched t.v's or music where its at?