I'm rural, and my area is subjected to power spikes, dips and outages. Some years ago I bought a Belkin PF60 (https://forum.audiogon.com/discussions/review-belkin-pure-av-silver-series-pf-60-ac-filter) for the surge protection, not any power "conditioning" designed to make my system sound better.
After some time, I noticed I was getting a very faint, low-level hum/buzz at system idle with no audio or video signal passing through the system, and eventually figured out that my cable box hadn't been routed through the Belkin's "Cable TV In/Out" connections (my system doubles as HT/2-channel). It was just HDMI-connected to the A/V receiver. Re-routing through the Belkin eliminated the background buzz without any noticeable change to any video/audio signals.
FWIW
After some time, I noticed I was getting a very faint, low-level hum/buzz at system idle with no audio or video signal passing through the system, and eventually figured out that my cable box hadn't been routed through the Belkin's "Cable TV In/Out" connections (my system doubles as HT/2-channel). It was just HDMI-connected to the A/V receiver. Re-routing through the Belkin eliminated the background buzz without any noticeable change to any video/audio signals.
FWIW