Hi!
The Foundation can't explain why the so called black birr turn up against all probability. There are to many occasions of ships being hit in deep space far away from gravity wells and far more often in ships with out temples or chapel-modules - as if the Icons suddenly would strike against certain ships.
They could of course publish studies saying, its just a micro-meteorite but the common folks and plebeians would know it isn't true and make this sign against the Dark between the Stars - at such blasphemy.
Hadra clouds are even weirder...
Hope that answers your question