What causes interference received as a series of carriers at regular intervals across a wide frequency range?
Why A switching power supply chops DC at a fixed rate, typically tens to hundreds of kHz, and the sharp switching edges generate a long series of harmonics of that switching frequency. On the receiver those harmonics show up as evenly spaced carriers, often called birdies, at intervals equal to the switching rate, spread all the way across HF and beyond. The key clue in the question is the words 'regular intervals,' which points to a fixed repetitive switching rate rather than a random or bursty source.
Watch out Electric fences are a common noise source too, but they produce a broadband pop or buzz repeating about once per second in time, not a comb of carriers at regular spacing in frequency. Radar and wireless cameras occupy specific microwave bands and would not spray evenly spaced signals across the HF spectrum.
Regular spacing in frequency = harmonics of a switching rate. Think birdies every few tens of kHz from a switch-mode supply.