I've actually read various threads online about Ranger whining but I haven't found anything that exactly seems to describe what I'm experiencing. And I need some help!

1. Yes, I have the power steering whine, but I've accepted that.
2. This is a yowling that has grown louder over time. It's not just a high-pitched whine, its a much louder yowl, in addition (it seems) to the power steering sounds.
3. It rises in pitch as I accelerate, and starts low and rises in pitch every time I shift gears.
4. But it recedes when I depress the clutch pedal.
5. Release the clutch and it yowls again.

Any thoughts? It just doesn't seem like it could be something attached to the engine if it shuts down when the clutch is depressed and disengaged. Could it be the differential?
I thank you profusely for any wisdom on this.