Which of the following could be a cause of interference covering a wide range of frequencies?
Why An arc is a rapid, repetitive breakdown of air that switches current on and off in microseconds. Those sharp, fast pulses contain energy spread across a huge span of the spectrum, so arcing at a loose power line connection, a corroded ground clamp, or a bad tower joint shows up as buzzy noise from the AM broadcast band up through VHF. Narrowband problems, by contrast, come from oscillators or harmonics that land on specific frequencies.
Watch out Skipping a balun or line isolator does cause RF on the feedline shield and can create interference, but that is your own transmitted signal appearing where it should not, not broadband hash across the spectrum. Rectification at a corroded joint can also mix signals, but note the choice about rectification says 'lack of' it, which would be a good thing.
Fast sparks make wide noise: an arc is a broadband transmitter you never licensed.