The 'Air-Horn' on 4020 is not radiating it's normal signal; there is plenty of carrier but the modulation is a weak 'prrrr-prrrr-prrrr' instead of the normal strident tone. Sounds 50Hz-ish.
Coincidentally the buzzer on 4625 is almost completely off air- it was very weak earlier and now it's almost completely gone, no carrier just a bit of sidebands. I'm struggling to believe its just bad propagation, I've never heard it that bad before and everything else seems normal.