Sub making electrical noises when connected to a Power conditioner

You’re on the right path to isolating the problem. What else are you plugging into the conditioner? Try eliminating a component one at a time while the sub is plugged in to see if the noise disappears. Are there any high current plug options on the conditioner for you to plug in the sub? Try one of those.

if the noise dissipates when plugged into the wall, then it is definitely one leg of a triangle of connected devices. This part of the triangle is the conditioner and sources. What outlet is the conditioner plugged into? Is it shared with other devices? Is it a dedicated 20 amp circuit? Try plugging the conditioner to another outlet. You can try just a simple multi outlet extension cord to see if the noise comes back with just a simple multi outlet extension cord. If so, then perhaps your sub is sensitive to some of the electrical characteristic of a multi outlet conditioner or extension cord. What brand and model is your sub? How old and how many watts? If the conditioner is not rated to support 1500 or more watts, than the sub amp and conditioner will get hot and may cause some electrical anomalies.

Ah ha. I had a loud hum through my subwoofer swarm for two months, I thought the Dayton amps were a problem, (recent thread on them not being able to find replacement parts). I had both amps plugged into the amp section of a Furman ref 20i.  If I unhooked my usb from my server or dac the hum would no longer exist. 

I finally decided to find this issue, the first thing I did was plug them into the other side of the conditioner and just like that the hum was gone. Try another outlet on your conditioner and you may be surprised! 

Most conditioners are not designed for use with power amps. Just don’t do it!

The furman 20 i have 80 amp or so reserve for amps.must have some caps in them. I would plug directly in wall but power spikes at least 2x a wk.so the furmans have kept amps safe.usually analog separated from digital on power banks on filters so they don't cross contaminate each other.happy hunting.hopefully the hum is not coming from rca cabel.the xlr can cut some ground loops out.

Fwiw I have two big 16 inch active subs.  They are, by far, happiest plugged into just a nice Furman surge protector and each with their own circuit.  It’s just too much power sometimes.

Whatever causes it, don't do that.. 🤪

You solved your problem by plugging your sub directly into the wall and bypassing the conditioner. My guess is that your amp(s) is/are plugged into the conditioner as well. Most listeners are against running their amps through the conditioner. I would try plugging the amp into one wall outlet, the sub into another if possible.