2001 BMW 325 fan clutch

Engine Cooling problem
2001 BMW 325 6 cyl Two Wheel Drive Automatic 145000 miles

i have just replace the water pump and have put everything back the way it was. Now its making a loud blower type sound when I step on the gas pedel. On the fan clutch in the center I thought there was a nut holding the fan clutch, so I removed the rectanguler plate that was in the center. Was that plate nessessary for the fan clutch? And how can I tell if it needs to be replaced?