Mine only does it on the drivers side,
has since it was new, I think the body
is a little out of alignment, even with
the new red replacement door, it does
the same thing, so I think it's in the
body or the way the hinges attach to
the body, I got the hinges from the other
Kick too, so I think it's the way the body
was made

Wild

I think the body
is a little out of alignment,

What, I could not imagine someone on this BBS having a tweeked body

I just got my '89 softtop 'kick running and ran into the same problem. I noticed driving on HWY 1 in Monterey that the driver door  was shaking like crazy. I also noticed the weather stripping outside of the kick near the top was loose.

When I got off the freeway for gas I pused the rubber back in place and never had the prob. Maybe you have a leak in the stripping.

Scared the sh*t outta me since this was the first ride over 60mph and I was headed camping in Big Sur for the week.

No, the weather striping is in there, but
don't stick your finger into the gap, it
kinda pinches and hurts

Wild

my girlfriends 89 2 door doors shake like your describing, only since putting on the ghetto swamper bias plys tho lol  .. also hers is a tin tip so if your doing over 110 KM/h the top goes BANG and pops up and then pops back down at 80 lol.. scared the crap outta me first time i heard it