Even after putting in a power conditioner, a customer had noise issues detectable with the meter which was helpful in finding the primary source of the noise--stuff was unplugged around the house until the noise source was found (a string of LED lights in a bedroom on a completely different circuit from the stereo).
@larryi - It is exactly this sort of issue why I don’t put a lot of faith in dedicated circuits or heavy duty wiring for noise reduction. I use Furmans which have filtration down to around 3kHz. Not perfect but a lot better than pure EMI/RFI filters. I wouldn’t mind having a dedicated circuit for the sake of power stability but my regulator does a very good job.