LIne noise analyzer....anyone use one?

I have a non contact A/C votage detector.
And have used it to find stray voltage.
It is somewhat similar.
Agree finding stray voltage and eliminating it is good for the stereo.
Mine was like $20 from Amazon: Greenlee GT-16. Works well.
Some of the other cheap ones are not as useful.

Another tool some use is the Grundig G8 radio.
It IS just a portable radio, but it is apparently useful for searching out stray frequencies..
I never used one, just mentioning it
Google it if interested in it's use.