Drive-line noises

[old cool]

Hello. My name is Ted. I am a new to this forum/site. Recently purchased a great looking, 90% restored 1966 GMC swb. User name: "old cool"

I have enjoyed reading various threads. There are tons of good questions and/or words of experience that we can all benefit from.

Question: What are the possibilities for drive-line noises that permeate the inside of the cab? I'm not referring to road noises that come from a truck that originally came with little to no insulation (or am I?). The most significant noise (whirring or whining) comes between shifting and and then while driving is 3rd.
Notes:
1. I've repacked wheel bearings and correctly adjusted same.
2. The seller said he replaced rear axle seal and found no evidence of ring and pinion deformities or shavings. He did suggest that "pinion seal behind yoke may be too tight" (his words). He also changed rear end fluids and repacked bearings. He also indicated that the whining noise was same before and after he performed the work.
3. Seller said it had Timken bearing upgrade.
4. I attempted to lube the u-joints. Couldn't get front fitting to accept lube and rear fitting in not accessible unless you remove u-joint.
5. The sound is more central to cab. It doesn't sound front or rear. But I realize that could be deceiving since sound has a mind-of-its-own on an non-insulated vehicle. Looking forward to feedback. Have a great day!