Well, life got busy and I'm finally getting back to this thread. I finally got the car in to look at the warble and took the mechanic for the test drive. Initially he had a hard time to hear it but eventually he tuned in and he definitely said it wasn't right.
He drained the differential oil and found it slightly low and replaced it and topped off. He took it for a test drive and didn't hear it. I took it home and it was much better but still a faint warble. The next day and ever since I haven't heard it again. Mystery solved for my car, for now anyways!