Dale
Interventions won't work
I second Nanci. This is poop, have you been feeding large mice or "fat" mice/rats? We have seen this kind of poop before when mating season is well over. Its basically fatty poop, hence the the urate.
Buzz
Yep, come to think of it, the most recent came after a meal of 2 rat pinks. I cant say for sure that that is what the other had eaten when he produced the same, but its a possibility. They're usually on mice, so that would explain me noticing the difference in appearance. We'll do some variable elimination feeding trials and see if we can prove this definitively.