It isn't just accents or mis-pronunciation or a palpable lack of competency in aviation English that annoys me (although I do find it very annoying, especially when I don't get a reply after politely asking the offending station to "say again"), but radio transmissions which are inaudible because:-
i) the equipment needs repair (e. g. lack of modulation depth), or
ii) the transmissions are masked by alternator-whine or the cyclic whine of strobe inverters winding up.
That really annoys me because it points to a need for some radio/aircraft electrical system maintenance which isn't happening. If that maintenance isn't being done on those aircraft, what else isn't being done?