Laserjet print banding

Hi

More printing problems:

Our company uses a HP 4650dn colour laserjet printer.

Several weeks ago, and today, some of the colour printing has had a defect. Photographs display limited orange banding down one side of the page.

http://img215.imageshack.us/img215/8414/band3qg.jpg

The banding generally occurs at 10cm intervals, though on the example above it occurs at 3.5cm intervals.

I have tried using different applications from different machines, using different images. I have tried printing when the printer has been used intensively and after it has been idle for 30 mins.

I have printed the HP print quality test pages and all are fine.

Does anyone have any ideas what may be causing this please?

Thanks