Three short lines, and the speaker is talking to a fly. The title, "Buzzing," sets up the joke: the fly's constant droning is pointless noise, and the speaker seems to recognize something familiar in it. The key line is the last one, "a rant is all din / and no ear." A rant, like a buzz, is loud and relentless, but it doesn't listen to anyone. It only broadcasts.
So the poem works as a small comparison. The fly becomes a stand-in for anyone who rants, and perhaps for the speaker too, since the opening "O fly" has the tone of a mock-solemn address, as if the speaker is half teasing and half sighing. The word "ear" also plays against the fly's tiny, bothersome presence: something that makes so much sound but can't take any in.
The mood is wry and slightly weary. It's light on the surface, but there's a quiet jab underneath about how noise can drown out any real exchange between people.