Old Dodge trucks are plagued by this too. If the trans is already modified to pump in park, then It's a combo of slop tolerances in the driveshaft (slip joint), and the pinion and ring gear. IMO, it's annoying, but harmless.
I had a trans with modified valve spool that pumped in P.
Iwarmed that baby up on a -15 degree day the last 10 minutes at work.
Left, put it in reverse after kicking down high idle, backed up normally, put it in drive, and at that moment the rear clutch pack welded.
No more reverse...only ever forward.
That was a fun February.
I'd much rather have the slow fill soft engagement, but then I always backed into garages in Chicago so I can't think of when I would have had a car sit for a long time that I would be first be backing up...
Never, I reckon.