Evolution of system peak for one node of CCD5 in RGS1 and in RGS2 (other CCDs show a similar behavior). The sudden increase of the peak around orbit 110 (most prominent in RGS1) is due to a solar flare, while the drop around orbit 168 (also indicated for RGS1) is due to the change in bias setting. Cooling lowers the system peak around orbit 532, while the single node readout in orbit 1408 increases the RGS2 system peak.