High Pitch Squealing in Chinchillas?

So my female chinchilla has been abruptly squealing extremely loud and high pitched. It only lasts for a second or two and tones down like a squeaky toy near the end of the squeal.

I have read a few posts on here and blogs etc. on other sites but nothing seems to be fitting for what my chinchilla is doing. I have taken her to the vet twice and nothing has been found to be wrong with her.

I got her about 5 years ago as a rescue, she was presumed to be young maybe 3 years old, so possibly now around 8. I think she was fixed as I got her from the SPCA but I honestly haven't been able to tell over the years. She is always energetic and I do not have a male around her.

So what has been happening has been for about 2 years now. Its not often, maybe once or twice a month if even that often. Sometimes though it will happen a few times pretty close together, within 10 or so minutes. It mostly happens when she jumps down from one ledge to another.
What confuses me is it sounds like she is in pain, but doesn't act like it at all. She will just happily jump around afterwards. She hates her hips being touched but also doesn't seem to actually be in pain, more like it tickles and bothers her. And the vet said with xrays nothing appears to be wrong with her and she has fine mobility.

I read it can be because she wants attention but that also doesn't seem to be the case. A lot of the time she will just jump around or go sit in one of her houses afterwards. Anyways it appears to be common but I don't know if I should still be as worried as I am after all this time.

Thanks for any info :)