I have found this to be an older male guinea pig issue, but I've heard it can involve younger guinea pigs as well. i don't make a regular practice of cleaning them out, but this video causes me to think I should keep a closer eye on things down there for my current boar.
I have been breeding rabbits for a quite a few years. I thoroughly enjoy them as animals and think they make great pets. I also like to take some of them to rabbit shows to see how they measure up to the standards.
For the BEST rabbit forum I've ever found. Go to Rabbittalk.com. Good for the pet rabbit owner as well as the breeder for meat or show.