A4 Rear End Noise

[Belpaire at aol.com]

Hello,
I am currently in the process of buying an automatic (Tiptronic) 98 A4 2.8 
Quatto with 30,000 miles on it.  During the test drive I noticed a definate 
whiring sound from the rear end.  The sound happens immediately after the car 
shifts into 4th gear.  As the RPMs increase so does the sound until around 
2000 rpm when it starts to tail off.  When decelerating through the same 
range the sound is also present.  

The dealer says its the tires or a bearing but I don't buy it, it really 
sounds like gear noise to my ears.  They say when I pick up the car it will 
not have the sound.  Is there any sort of recurring problem anyone has 
experienced a similar problem like this?  Is there anything I should look for 
about this and should I be overly concerned about it reoccurring if the 
dealer is successful in eliminating the problem?

On a related not, the dealer also says the car has the sport package, but it 
has 5 spoke wheels.  Did any 98 A4's with the sport package come with these 
or were the 7 spokes the only wheel that came with the sport package?


Thanks in advance,
Roger Hahn