Litter trained pair peeing on floor!?

I have a male and female and they are a year old. I have had the female for a year and the male we have had for 6-8 months. The are both fixed and have gotten along great from the start.

They are in an NIC cage with an xpen attached for more room. We keep them in there at night and while we are not home but they are free to roam the house when we are home.
the xpen has a carpet rug under it and it has worked well for 6 months but now all of a sudden someone is peeing on it.
I cleaned it thoroughly hoping they would go back to using the litter box but it isn't helping.

The female is kinda bossy from time to time, mounting the male any time she thinks he is being rude so now I am wondering if she is the one peeing and is it a territorial thing?

Help please!!! What can I do do get them to stop peeing on the floor?!

Has there been any type of change? IE litter change, box change, new pet/animal in the house?

Also, is it carpet meaning attached to the floor or is it a rug you just have in the xpen?

No, No new changes. Litter box is same as always. No new animals or anything. routine is the same. they get plenty of exercise everyday. and they both seem healthy. I thought maybe it could be a bunny uti but they both seem fine.

Oh and the carpet is just a rug that sits under the xpen. If I remove the rug then they will not come out of their cage.

I was going to suggest removing the rug. If not, make sure it is cleaned well. I like Natures Miracle to get rid of odor.

Also, place more litterboxes out in the xpen area until litter habits resume then you may be able to remove them again.