Update:
I took some videos regarding the play. Both are with the truck in gear.
The slip yoke has some slop, but not excessive I think. I switched the drive shaft on the yoke 180 degrees but did this not have any effect on the noise.
Slip yoke link:
https://youtu.be/7CverabZ7Kk
The rear end has a lot more play though. But it is a total play, as the floating axle splines probably have some play as well, as do the gears inside diff. The pinion shaft is really tight, with no up and down slop or axial play.
Link:
https://youtu.be/nKUeE7NV5gc
Any thoughts?