Something bad is starting to fail.
I would open a TAC Case and RMS the device.
Try this (with example outputs shown)
Router# show environment
Warning: +3.3 V measured at +3.41 V
The show environment last command retrieves and displays the NVRAM log, which provides a record of environmental status readings. Air temperature is measured and displayed, and the voltage supplied by the power supply is also displayed.
Following is sample output of the show environment last command:
Router# show environment last
chassis core previously measured at 34C/93F
chassis inlet previously measured at 28C/82F
chassis outlet 1 previously measured at 31C/87F
chassis outlet 2 previously measured at 33C/91F
+2.5 V previously measured at +2.59
+3.3 V previously measured at +3.32
+5.15 V previously measured at +5.13
+12.3 V previously measured at +12.99
+12.3 V previously measured at +12.33
-12.5 V previously measured at -12.43
The show environment table command displays the temperature and voltage thresholds for each temperature sensor and for each monitored status level, which are related to those thresholds listed in Table 6-1 and Table 6-2.
Following is sample output of the show environment table command:
http://www.cisco.com/en/US/products/hw/cable/ps2211/products_installation_guide_chapter09186a008007de28.html
Hope this helps
