Whining Noise while coasting downhill

[nboswell]

I have an automatic 2002 Chevy S-10, and last weekend it starting making noise while coasting downhill at >50 mph. It is a whining noise that sounds like my tires are spinning out, but it is completely dry out.

The noise stops when I put any pressure on the accelerator or when it is put into neutral. Along with the noise, the rpm's drop.

First thought was wheel bearings, but that would likely continue to happen even in neutral. Next thought is a transmission problem.

Any thoughts?