I read a humorous science fiction story some ten to twenty years ago about robotic explorers who discover a planet, perhaps Earth, with intelligent organic lifeforms and can't quite believe it. They argue about how impossible that is. Apparently all intelligence in the galaxy is machine-based.
In the end, I think, they decide against contacting the organics. Nor do they tell the rest of the galaxy about their discovery because they won't be believed.
Any clues?