Omg! I'm so glad you posted this because one of my rats does the same thing.. or at least it seems the same. I posted about it a while ago, but I don't think I was able to describe it very well.
Is the "scooch" sound soft - because that's sort of the noise that Sachi makes. Hers is somewhere between the "very soft basketball squeaks" and a soft whimper. She only does it at night though, usually when she's eating.
Keep me posted, lets keep comparing! In fact, I recorded the sound on my computer, I'm just trying to figure out how to share the file.