Any automatic trans guys here?

So my tranny shifts fine, I have no complaints, but I do hear some slop(?) in neutral that goes away when I put it in gear. I also hear this slop when under no load, and coming to a stop. Sounds like big poker chips being mixed up.
Once there is a load as I come to a stop the noise quiets. Sitting stopped in gear with my foot on the brake there is no noise.

As far as I can tell there is no issue, but I don't think a fluid filled device should make this kind of sound. It's a 48RE with Goerend internals.

Any ideas?

This thread is probably in the wrong forum. Sorry about that.

I found this in the service manual and I think it's relevant.

(Short translation of below is take it to a good trans shop)

Engine running, in park=noise

When the gearshift lever is moved into the DRIVE
position the transmission goes into first gear.
As soon as the transmission is shifted from PARK or
NEUTRAL to DRIVE, the rear clutch applies, applying
the rear clutch pack to the front annulus gear.

Noise goes away

Engine torque is now applied to the front annulus
gear turning it in a clockwise direction. With the
front annulus gear turning in a clockwise direction, it
causes the front planets to turn in a clockwise direction.
The rotation of the front planets cause the sun gear
to revolve in a counterclockwise direction. The sun
gear now transfers its counterclockwise rotation to
the rear planets which rotate back in a clockwise
direction. With the rear annulus gear stationary, the
rear planet rotation on the annulus gear causes the
rear planet carrier to revolve in a counterclockwise
direction. The rear planet carrier is splined into the
low-reverse drum, and the low reverse drum is
splined to the inner race of the over-running clutch.
With the over-running clutch locked, the planet carrier
is held, and the resulting torque provided by the
planet pinions is transferred to the rear annulus
gear. The rear annulus gear is splined to the output
shaft and rotated along with it (clockwise) in an
underdrive gear reduction mode.

Could it be as simple as a worn universal joint?

I don't think so. I've looked and they were tight. I get no clunking or vibration. If it weren't for the clatter in park/neutral I wouldn't even mention it. Function wise I don't notice any problems.

I just saw the thread title and said “here we go again” LOL

shhhhhh ..... they are watching us.