I might also have to do a bit of sanding on the bottom edge of the glass, as it has a bit of a sharp edge. I'm worried that the girls might cut the bottom of their feet if they are standing up and resting their front paws on the edge of the glass, when begging for food. This sometimes happen when I bring them vegetables and open the cage door.
We had Abigail to the vet yesterday to get a look at a small lump she had on the side. I had the vet do a follow up x-ray on her to check for stones, before committing to the experimental treatment discussed earlier, and there was nothing to see! I'm so happy as I was really worried that new stones had formed already. I'm also a bit perplexed regarding her squeaking. It still happens every now and then, sometimes I notice it once a day, sometimes like 3-5, other days there's nothing. She still seems happy, and like herself, eating and relaxed. It was the same years ago, if I remember correctly, when we first started to notice.
The vet removed the small lump, but it was such a small operation that she was pretty ok when she came home. Almost started to eat instantly. The most important thing is that she's ok :)
I took a picture of Abigails pee the other day as I heard her squeaking a bit and went to have a look. I have marked the pee with a red ring, but it's a bit hard to see at a quick glance.
I can't tell much from your picture. To check for sludge, a medium or dark colored cotton cloth helps a lot. It is important to note that pee changes depending on what was recently eaten (or at least it seemed to - I used to see substantial piles of excreted calcium [not grit, powder] a while after eating romaine lettuce). So it could be relatively clear one time and could include lots of excreted calcium the next.
Sludge should also show up on an xray if present. I am guessing that for a guinea pig that had a problem with sludge, it would depend on how much there was and how efficient the guinea pig's body is at excreting it. Increasing fluids and vibration can help suspend sludge and encourage excretion.
So stones (more likely) and sludge are two conditions that could account for the squeaking. Could also be something else.
Check out Tracis' links to information about interstitial cystitis:
Regarding the plexi glass. Do you guys think that sanding the edges is necessary?
Glad to hear things are improving!