If this part of the post is the only time you notice this problem and its brief I would disable the logo screen and see if you still have problems after XP loads.
Stress the 1600 with 3Dmark 2006 or check for artifacts with ATI tool.
Remember that the ATI drivers are not even loaded until late into the boot up in the windows environment.
If this happens under all conditions then I would agree that the card may be defective.
Otherwise the brief glitch may just be a spike from that power hungry card during initialization.