The ONLY cure for RF (radio-frequency) interference is a Faraday cage; however, as others have mentioned, RF is hardly likely to be the culprit. Most likely, it is EM (electro-magnetic) interference rather than RF. As someone has mentioned, transformers related to other equipment are likely to contribute to audible
60Hz (and harmonics) noise. And, if your system is improperly grounded (or there are ground loops) it is extremely easy to have that noise induced into your signal. Likely culprits are the power supplies associate with low-voltage lighting (often halogen and/or LED), florescent lighting, door-bells, and some of the smart-home controllers that inject additional signal on top of the A/C line.
Given that most high-end gear-heads tend to spend ridiculous money on various interconnects, that is an unlikely problem. Some (poorly designed) preamps do not ground or terminate un-selected open inputs, creating a possible source of noise induction. Speaker cables, also, can pick up induced hum.
Cheap but VERY effective speaker cable formula:
- Purchase a length of 2-conductor, 16 gauge, stranded copper lamp cord that is EIGHT (8) times as long as needed for your speaker cables.
- Purchase terminators (spade lugs, banana plugs, whatever) appropriate for your amp and speakers.
- Cut the lamp cord into SIX (6) pieces of equal length. They should be about 20-30% longer than you actually need to cover the span from amp to speaker.
- Solder or clamp three of your new speaker cables to the terminators for the amplifier, making sure to observe polarity.
- BRAID (like hair) the three cables together such that you get approximately one complete braiding cycle every four inches.
- After braiding, solder or clamp the remaining ends to the terminators for you speakers, again, making sure to observe polarity and adjusting cable length to shorten if needed.
The reason for the 8X length versus only 6 pieces is that braiding shortens the effective length of the finished cable.
The resulting speaker cables can carry more current (and voltage) than even KW-rated amplifiers can produce. Moreover, they are as immune to induced signals as anything commercially available without going to shielded conduit. And, they cost relatively nothing. Win-win!