Actually this is not the problem it once was. FCC regulations for the past 25 years or so have placed strict limits on conducted and radiated emissions from electronic devices not specifically designed to radiate, especially for devices (Clas B) intended for residential use. The same technology that bottles up energy inside the devices is also quite good at shielding devices from external sources. Equipment that predates those regulations almost invariably has problems with interference from multple sources.

Generally good equipment design goes a very long way toward eliminating the problem. I used to design and build equipment that had to be tested on a test range to insure FCC compliance. After a couple rounds, I learned what tecniques worked well and what didn't work so well. That cut down on our testing expenses condierably, since we didn't have to repeat visits to the FCC certified test range.

The difference between such regulations and not having them is often quite striking. For example in many countries, you can tell when a GSM mobile telephone is about to ring because of the interference produced by the 217 hz transmission rate on many inadequately shielded electronic devices as the call is being 'set up' with the hand set.