Hey Zooey!
How long have you had Perry for?
Chibi, my budgie started making noises just like that a couple months back. It sounds just like what you've described: a warbling sort of guttural grumbling mixed in with occasional squawks and such.
I'd say that you might soon have a talking budgie on your hands
A couple months of that noise and then my budgie suddenly started talking. One day as I was walking by he suddenly piped up and said: "Hey Chibi!"
I figured the grumbling/warbling noise was him trying to figure out how to form the new noises.
Chibi doesn't ever make that grumbling/warbling noise anymore unless he's trying to figure out a new phrase.
Hopefully this might be the case for Perry as well!