Front end help with rumble noise

[pjm]

I'm trying to fix a rumble noise that I have on my 96 Explorer. It's coming from the front end. I've been driving without a front driveshaft because I took it off last winter because I couldn't stand the rumble and vibration on the highway anymore. When I pulled the shaft the rumble and vibration went away. So I think I have a bad shaft. New shafts are $300. Winter is around the corner here in in MN, so recently scraped it together and bought a new shaft from OReilly. Installed and took for a drive and the rumble is back. Not noticeable at 30-40 mph or less, but becomes evident and progressively worse at about 50 mph. It also doesn't seem as bad as I remember, but still bad enough to need fixing. Only notice it on the highway. Sound makes me think of a bearing going out. I've replaced both hubs and both front cv axles over the years. It has a brand new driver cv axle that I just changed due to a torn boot. The whole axle was only a little more than the boot replacement so just swapped it out.
Is it possible I'm looking at a bearing issue with the transfer case output shaft, the front pinion bearing, or the front torrington bearings for the cv shafts? How do I pinpoint for sure? There is no obvious play at the TC or the pinion. Should I go ahead and change out the passenger cv axle just to remove that as a possible source? :scratch:Thanks in advance for any ideas.

 

[pjm]

Pulled the driveshaft back out and noise went away - or at least I didn't notice it anymore. Checked for pinion bearing play - none. No leaks at pinion seal. Checked for transfer case output shaft play - none. No noticeable leaks there either. Checked the wheel hubs (which are relatively new). No play top to bottom (12 to 6) but significant play side to side (3 and 9). Of further inspection, hub is not the source of the play but the rack appears to be. Front end was completely rebuilt with all new components around 20-30k ago (except the rack). So could the play in the rack be inducing this high speed vibration only when the front driveshaft is on? Could the additional mass somehow be introducing vibration where it is not noticeable without it? In any case there is a rack and pinion in my near future. Guess I'll install that and try it again. After I drill out the bolt that snapped off in the pinion flange for the driveshaft. Argh.