I've been a ham operator since I was 10 so I have a little experience on the subject. Interference can come from anything. Lots of power supplies for surprising devices are culprits. The little cheap universal AC/DC adapters are one of worst offenders. Power-lines, bad transformers, any business that has massive electrical devices.

TV's, (especially older) microwaves, vacuum cleaners... pretty much anything can cause interference. One of the worst culprits are the cordless handsets.

The biggest offenders aren't devices that use the same rough frequencies, it's ones that either splatter all over the place or have harmonic issues (multiples of frequencies, a 500MHz device can splatter 1,000MHZ, 1.5GHz, etc)

It would be nice to have more spectrum for use for digital devices. Hopefully in the US they continue moving the TV stations off and eventually provides more spectrum for growing wireless devices.