Please help me eliminate the hum my digital rig creates

Thanks very much for your responses. Everything was plugged into the same outlet-- the integrated into one receptacle and the power conditioner plugged into the other. The DAC's PC is a Revelation Audio Labs Precept 2, which is designed for sources and I have to assume it is shielded.  I upgraded the Vault’s C7 to a Pangea shielded cable.

However, when I took ADG’s suggestion and plugged the conditioner into another outlet, the noise remained. In fact, even after completely unplugging both the DAC and Vault from any power source, the hum remained. I finally sleuthed the noise to the ethernet cable from my modem to the Vault. As soon as I remove it from the Vault, the noise disappears. The cable I’m using is a 12’ CAT7 with shielded ends:

https://smile.amazon.com/gp/product/B01N8QJRZ9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

We’ve been having modem issues so it’s about to be replaced. I’m hoping the same thing that is causing connection problems is causing the noise. I’ll likely know by this afternoon. If the noise persists, maybe I should get that placeholder power strip ADG suggested for the modem? Perhaps there’s a better-shielded ethernet cable you could suggest?

I’m only using the Belkin because the (admittedly low-end) Monster Power conditioner I had died and I had the Belkin lying around. I’d be happy to buy a decent conditioner if that would solve things, although my personal calculus makes purchasing a $3.5k conditioner like the P5 in a sub-$15k system seem a disproportionate expenditure. The Audioquest Niagara 1200 seems to occupy a sweet spot both in terms of size/shape for the application and price.

Thoughts?

We had the modem replaced today and every other component remained the same plugged into the same place and the hum is completely gone. It was just a faulty modem that began to generate hum when it went bad. In response to Jea, I live in Manhattan in a large apartment building, so all grounding issues are out of my hands and only licensed professionals are allowed to work on anything in the building.  NYC’s department of buildings views property owners as a huge source of income through penalties and fines so I’d be surprised if everything wasn’t strictly to code.

Thanks everyone for their thoughts and time spent responding to me. If you hadn’t asked the questions you did, I wouldn’t have been inspired to get more scientific and really eliminate each possible cause of the noise to discover its source.

Congrats! Glad you found the culprit. I had a modem do that to me too, although it somehow started pouring audible rfi into my tube preamp. Bizarre when it happens suddenly.

Sorry *router* not modem.