...455kHz...?? Can't imagine it's anything special.
Sounds like breakthrough to me... bear in mind this is AM we are dealing with. Only happens on one freq, lots of loud background noise etc.
Ferrites can be useful, just bear in mind you have to pinpoint what to stick your ferrite on (don't whack them on everything) and also to get the best results you will need to take at least one coil around the core. Also bear in that this won't work with coax cable (ie the aerial cable)... which is where it may just be coming from!.. either that or on the audio lines...
