Sounds like a loose connection on a socket maybe? If it keeps up complain about it while it's still under warranty.
Glad to hear the tap on the fan worked - I hope it stays quieter now.
If you're located in the US (?), and not already familiar with Pinky at Red Sea:
Pinky Bulot U.S.A. Office: Red Sea 18125 Ammi Trail Houston, Texas 77060
Tel: (281) 447-0205 Fax: (281) 447-1153
Toll Free: 1-888-RedSea9
pinky@redseafish.com
or
redseainfo@redseafish.com
Pinky has been a great help to a lot of us in the US and Canada and your best bet when you have a problem would be to either call the toll free number or send an email to Pinky at the above email address. A phone call usually gets the best and quickest results.