Cairo and Cuba are victims of old Soviet era transmitters and no new parts for decades. The audio sections had to withstand years of Fidel and Nasser ranting as loud as they could for hours on end. It takes a toll. The heat and humidity of Cuba, plus the 2-4 hurricanes a year don't help either.
Iran sounded ok up until the early part of the century. Their transmitters are from the time of the Shah. I guess the frying pan heat caught up with them? Anyway, it's all sermons and prayers, everyone memorizes them in religious school, Son of Satan.