First you have to check the counters to see how many pages were printed or copyed. It may be a problem with some of the color drum units. At this model you need to change the units near to 100.000 A4 prints with 5% coverage. If the coverage is greater, then you'll need to change them sooner. There might be another cause for the sound, like the Transfer Belt Unit. This unit has a "waste toner path" that might be jamed. The unit is not able to get rid of this waste toner and some gears produce that noise. The transfer belt unit is working separatly for black prints and color print. You will have to remove the Transfer Belt Unit and clean the toner path with a vaccum cleaner.