Interference is a constant in the universe. It varies in quality and quantity but there is always some. It's ever-present, and is just part of the deal in radio. Noise happens. Most interference when it appears has a pretty clear source, or is at least only audible over a small area. The source may be novel , or mundane but the list of interference sources is fairly manageable.
In November of last year we had a mystery on our hands in radioland. There was a 1Khz tone reported on the frequency of 590 kHz on November 27. Then a day later it moved to 1610 AM. Apparently unhappy messing up WIBG-AM in the expanded band, the tone moved 1020 kHz. While the tone interfered with little other than CHHA-AM on 1610 in Toronto, and was a minor offender on 590. On 1020 it was a problem. While initially reported in New England, it was also reported as far away as Florida, Oregon, Arkansas, and Scandanavia!.
Engineers and DXers began to examing the tone, and take signal bearings to locate it's source. Guesses ranged from New Jersey to North Carolina. As the geeks moved in, it moved out. The tone jumped from 1610 to the far more problematic 1020. It now interfered with the 50,000 watt powerhours KDKA-AM in Pittsburgh.
There have been reports that it's an experiment by the goverment on co-channel interference, it's a psyops project, it's a propaganda transmission to Cuba, it's an alien message! The oogily Boogily stuff is amusing, but I can say that this is unusual in it's total lack of any kind of ID. the FCC does approve experimental broadcasts on the AM band. But these are limited to the 0100-0600 hours, and the ID is mandatory.
I've seen no paper work on it but it's been reported that BAE Systems had applied for an experimental license for testing mobile broadcasting systems. The original application had requested 590, 1020 and 1600 kHz using 10 kw of power from Fort A.P. Hill, near Bowling Green VA. Thsi is as yet unconfirmed...