Worried - Blood Found in Cage

Hi everyone,

I have two female chinchillas who have been together in the same cage for 3-4 years now. Recently, we have been intermittently finding spots of what looks like blood randomly throughout the cage. I have checked both of my girls for injuries and they have no cracks in their feet, their teeth are fine, and there is no blood staining the fur around their private areas. I also haven't been able to locate any cuts or scrapes on them. There are no sharp areas in the cage as well that could have cut them. This has happened a few times over the last couple of months but only seems to happen at night and we find the blood in the morning. I'm getting quite concerned because I don't know where this is coming from or what chinchilla it is coming from as well. I feel that separating them would stress them out quite a bit because they are very bonded and often cuddle with eachother throughout the day. I haven't noticed any changes in behaviour or eating habits either. Any suggestions as to what could be causing this? I have seen people suggesting to check paws and such, but my girls have very good paws with no cracks.

Any advice would be greatly appreciated