The thing that jumped out at me in your description was "I ... tightened the pinion nut good and tight with a 1/2" socket".
That jumped out at me too.
Pinion bearing pre-load is adjusted with shims, not pinion nut torque or a crush collar. If the pre-load is correct, the torque on the nut will not change the pre-load. What happens over time as the bearings and races wear, the torque on the nut gradually gets less and less. If one now retorques the nut, or tightens it good and tight, the bearing pre-load can be so high as to prevent the pinion from even spinning!
The trick to replacing the pinion seal is to first note the torque on the nut before
removing the nut. After seal replacement, torque the nut to the previous value (disregarding the torque spec in the book).
I'd wager the noise is excessive pinion bearing pre-load. To remedy this, remove the driveshaft and loosen the nut. Then tighten the nut by hand until there is zero horizontal, vertical and axial play in the pinion. Now note the resistance required to turn the pinion. Gradually
tighten the nut until the resistance starts to increase and stop there. Then lock down the nut.