Whine, Help!

[cdvs]

I've got it up on blocks. Little, if any, whine until it shifts into second around 25-30 mph. Then the faster the louder. Crawling under to listen, sounds like it's from the rear of the transmission. That is, the sound is equal to both ears when my head is below the end of the trans., or slightly toward the rear.

So, I decide to put in the FWD fuse. As expected, less noise over all, rears are not turning. Until it shifts into second. Then the whine starts and the rears start turning.

I'm baffled, please help if you can.