Line noise is a disruption of the normally smooth sine-wave pattern of the
AC mains. Some equipment is more susceptible to it than others.

It happens when things like old/faulty switchgear are on the line,
substation demand variation, in fact your own property can even be the
source of the noise.

Why not install a conditioner between the mains & your unit?

"Bob" wrote in message
. ..
I have an APC backup surge protected that keeps reporting that it is
falling over to backup power because it detected line noise. This happens
5-10 times a week. Anyone know what line noise is and what causes it?