1989 Carat Wolfsburg Edition
Automatic transmission, 2.1L engine.

At cold idle in drive, the engine has a lot of movement, enough to
rattle against the body at some unknown location. 
This is very annoying sitting at a stop light or stop sign.
If I put it in neutral at a stop light, the movement ceases. 
After engine gets up to normal operating temperature the engine movement
goes away.
Any ideas as to what is going on here?

The transmission is smooth otherwise, shifts nicely and when it is
supposed to. 
Engine is in tip top shape, heads were done at Eurocars not long ago,
and it idles fine, around 850-900 RPM.

Any help is greatly appreciated.

Andy