[blykins]

Jay, you sure it's the rearend and not the tranny? The tranny sits so far back, it could be it that you're hearing.

Let's ask some more questions:

1. Does it make the sound in 4th and 5th only?
2. Does it do it under full acceleration, and likewise when you let off the gas (coast)?
3. Do you know what your backlash and pinion depth are supposed to be? And what did it compare at when you had them readjusted?
4. Is your tranny old?
5. Are the bearings in your rearend new?

I'm thinking it's not the rearend...it's the tranny. Especially if you have a short-throw shifter like a Pro 5.0 or a Hurst. Those are extremely noisy and you can hear the tranny more profoundly.

If you were having problems with your rearend, you would get some other noises under acceleration and under coasting...probably along with some roaring sounds. I think the only thing that would whine would be bearings about to seize. If so, you could check this out when you pull the center section off the housing. The gears would be blued....or your rearend grease would smell burnt.

Hope this helps...

BTW, what tranny are you using?