HP Laserjet 4250,4350,4345 noise

Hi
I am a printer technician who would like to pose a question to other techies
out there.

I have a number of the above printers and I have noticed that they are
starting to make a noise by the gear that couples up with the fuser unit.
Now the fuser unit gear, the cream one, is not worn however it is covered
with debris from the gear in the printer. The printers have page counts
ranging from 6000 pages up to 70 000 pages. They are all under warranty.

I am very interested to here from you.

Regards
Henry Levine