Are my guinea pigs eating too much calcium?

I have two guinea pigs and I have been noticing the last few days that there are white urine spots on their fleece bedding. I have heard that means they are eating too much calcium or something?? What do I do? I feed them timothy hay pellets, carrots, romaine lettuce, parsley, cilantro. They really love carrots, maybe that's the problem??? Thanks in advance for your help :)