The dark currents of both types of EPIC CCD are negligible sources of background noise under nominal operating conditions (especially above 250 eV for the pn camera).
In MOS there are low level `flickerings' of a small number of pixels at an occurrence rate . Two peripheral CCDs of the MOS cameras (CCD4 on MOS1, and CCD5 on MOS2) are frequently affected by a low-energy (E1 keV) noise plateau, see Section 4.3.2 "EPIC-MOS low energy noise in two peripheral CCDs" for details. In pn occasionally (mainly during high particle background) the offset calculation leads in some pixels to a slight underestimate of the offset, which can result in blocks of approx. pixels with enhanced low energy signal.