I'm not sure how to help, since I don't know much on gerbils, but didn't I read something on your other thread about how they may do this out of stress? Are they still in the room where your cats are?
To reduce stress on all my rats, hamster, bird, and guinea pigs, I leave their cages in my room, and I don't allow the cats in there.
Whatever the cause of the problem is, I wish you luck.