As shown below, Swordfish shredders have 3 settings: Reverse (<<), Off (O) & Auto (I).
The Auto setting means that the shredder will automatically detect when paper is inserted and must be selected for shredding. If the shredder is set to Rev then it may appear to run continuously.
1. Check that the shredder is switched to 'Auto' and not 'Rev'. Has this resolved the problem?