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Is it a buzzing noise like the one heard at about 0:45 onward in this video?:
The error codes relate to a serious malfunction, possibly in the imaging unit. Some offer a reset for the imaging unit as an attempted remedy, others say it requires some serious repairs to the machine.
P-9 is listed as Cyan imaging unit failure.
P-21 is listed as Color Regist. Test Pattern failure.
Here are the pages from the applicable service manual:
The service manual for this machine might be very useful for this problem, esp. if it is severe and requires parts replacements. Here's a source to buy it from: