5V out-of-range mutes N3

Hi,
A unit has occasionally (over months) gone into a series of mutes.
Typical log entry:
11/6/2007 16:27:52 13844 note piond/mute unmuted
11/6/2007 16:27:52 13843 error piond/hardware_monitor +5V recovered: measured 4.764647
11/6/2007 16:27:52 13842 note project user logged off: clubav
11/6/2007 16:27:48 13841 note piond/mute muted: voltage out-of-range
11/6/2007 16:27:48 13840 error piond/hardware_monitor +5V low : measured 4.738468, expected 4.750000
11/6/2007 16:27:32 13839 note piond/mute unmuted
11/6/2007 16:27:32 13838 error piond/hardware_monitor +5V recovered: measured 4.764647
11/6/2007 16:27:28 13837 note piond/mute muted: voltage out-of-range
11/6/2007 16:27:28 13836 error piond/hardware_monitor +5V low : measured 4.738468, expected 4.750000

...repeated many more times.
This was observed 6 months ago while the system was running NWare1.1.3, then has not appeared for some time (with system running 1.2.5), but has had bursts of this behaviour in the last month, and now doesn't appear to be recovering at all.

Does this suggest PSU or motherboard?
Thanks,