Driveline vibration
Ultimately something fixed it enough that my dad stopped pestering the dealer.
I went back through my dad's noted.
Ultimately the dealer in the first 2 years ....
Replaced the ring and pinion
Replaced one wheel due to run out
Rebuilt the transmission
Replaced the driveshaft
And that was the last entry about the beat / howl at between 50 and 70.
His notes say:
"Test drive with factory man Leon Crady (Dad underlined name) up to Overland Blvd and back beat at 72 - howl at 65 back to Claude's up on rack. Leon looks at drive shaft - says it is twisted counter to normal. Looks to be a manufacturing problem, will replace. Will pull windshield to correct leak"
I don't have any info about how much it was off, there is info online about u joint angle tech and what happens if they are off.
Easy to check, with a long straight edge or maybe a chalk line.
I would suspect they if it was off by a degree or two there would be no noticable effect but 5 or more might.