I have an HP color laserjet 2550Ln. This week I replaced the black toner cartridge, but pages only print down the right side of a sheet, fading towards the middle, until blank on the left. There was a starnge "vibrating" sound as the carousel turned. I thought I might have a faulty cartidge, but replaced it with no difference. I have also replaced the imaging drum, still no difference. I checked HP's supprt online but their troubleshooting advice pretty useless. Any suggestions?