My suspicion is that pacing around and jumping back and forth across the cage is a territorial behavior to drive off intruders. I've had two that were really bad about this whenever someone they didn't know would come into the room. My grey, Kulu, is very strongly like that. My white mosaic, Spot, couldn't care less, so it does depend on the pet. Kulu got so bad I had to separate him from Spot last month. You can tell (if they have been introduced for a minimum of two weeks) to put them in the bathtub together with a dust bath. The dominant one will mount the other chinchilla. Make double triple sure they are all the same sex. Never let opposite sex chins play together. Keep an eye on food consumption and weight. Such behavior can indicate stress. You'll have to be judge of that.