I started noticing some really dirty eggs from my new flock, that recently started laying. As I did some detective work, I found they were mostly coming from my Cochins, whose long fuzzy butt feathers were getting clumped with poop. After I gave those girls a little feather trimming around their vents (mostly just where poop was stuck), I stopped getting "unusually" dirty eggs. May or may not be your problem, but worth checking!
