Auto tranny noise on A90

[Gregory Deschodt <GXD@synon.com>]

Hi there, 

New member here, but hey, I plan to trade in my Golf VR6 for an A4 soon
(ideally for an A3, but it's not coming to the states ).  This is
actually related to my fiancee's car. I convinced her to buy a 1991 Audi
90, super condition fully loaded. It's got automatic transmission,
unfortunately, and it does a funny thing: 
when slowing down (in Drive), at around 20/25 mph, the tranny drops to a
lower gear automatically (you can tell by the revs) and you can hear a
fraction of a second's tire screeching noise... Is that normal ? 

Is the engine so torquey that it actually spins the tires when going to
a lower gear ? The tires are new BTW.. Could it be something else ?  I
have never heard stuff like this before but then again I have never
owned automatic cars..

Thanks in advance !   Greg.