There was a thing in Britain called 'the Luxembourg fade.' it was a fading screeching sound that happened to the skywave on 1439 (later 1440) Khz when the carrier level became lower than the sidebands in a selective fade causing the sidebands to beat with each other. It seemed to only happen to Radio Luxembourgs skywave, I can't remember it happening to AFN or other skywave stations such as Radio Sweden. Not sure why RL was affected so bad. Always seemed to happen when your favourite song came on, lol...