Possible clutch/transmission issue

I have been through most of the clutch and transmission related posts and have not identified a similar problem to the one I believe I am experiencing.

I have a pulsating hum or singing sound coming from my transmission area at speeds above about 15 mph. It is similar in quality to the sound made by agressive tread tires on the highway but a little higher in pitch. The sound quits when I depress the clutch, and it returns when I release the clutch. It is also not present if I coast in neutral with the clutch released.

I did not think it was the TO bearing as the noise does not occur when the clutch is depressed. Thought it might be the TO bearing riding too close to or against the pressure plate fingers. If this is the case, I am clueless as to how I need to address the problem. I have properly adjusted my free travel to 3/4-1" of travel. All of my linkage components are new, correctly installed (I beleive) and to OEM specifications.

Any one have any thoughts or advice?

 

Trans full of oil?
I just did fluid checks last night and found my T case to be over full and my T-18 took 29 pumps to fill!

 

Yep trans and xfer are full.

 

Thanks much. I was hopin' it would be easier than that, but I may have to tear it down.