From my experience it is. Minx did this sometimes for a time after a lot of prodding by the vets, if I happened to touch her somewhere she'd been hurt. Kind of starts low and escalates into a full blown high scream, yes?
The quieter guinea pigs seem do it only after something REALLY hurt them, while the more vocal ones can get carried away a bit more easily.
I'm glad that Connie didn't have an operation; but I'm new to these boards, so I didn't catch the whole story.
When Minx was having a stone, she started with making low, a bit like mewling noises when she was passing crystals, or urine over a scratched bit of the uretra, or pushing a bigger stone into the uretra. Usually the urine was a bit reddish from blood. And she would make a round back from the pain and not curl up on her side when sleeping - that's when I knew we were due yet another trip to the vet again!
I hope that this description can help you to look out for more specific signs without getting worried about everything unusual that's going on!