When I was a kid, I regularly used a crude 6 tube Hallicrafters S-41G that belonged to my Father. (yes, I still have it, of course). This set has only a 2 gang tuning capacitor, hence had *no* tuned RF stage. Selectivity was poor, but sensitivity was ok, when using a long wire (approx 100 ft) outdoor antenna. It was great fun for a geeky kid!
Video "buzz" and garbled audio from a nearby ch 6, as well as garbled audio from several FM stations could easily be heard when tuning around above 20 mHz or so. I was told that this was caused by "local oscillator harmonics" generated by the radio.
The math seemed to confirm this theory... When tuned to, say 21 mHz, the local oscillator of a set with a 455 kHz IF amplifier would be tuned to 21.455 mHz. The fourth harmonic of 21.455 is 85.82 mHz which is right in the range needed to convert a segment of ch 6 (82-88mHz) to 455 kHz, which could then be amplified by the IF amplifier and heard. By tuning around a bit above this, several FM stations (FM band is 88 to 108mHz) could be heard.
jr