Make sure to do everything hieveryone mentioned and then:
1. post the results on the forums here
2. discuss and worry as much as possible with the rest of the community
3. Get a replacement from the apple store because you finally found an imperfection
4. Repeat the entire proccess until the apple store refuses any more replacements
5. Use other means to return your macbook, like sending it to apple via mail until this is refused, too
6. Write emails to Tim Cook until they grant you one last replacment
7. notice that your last replacment has a dent on the bottom, a yellowish tint, cranking sounds, image retention, a noisy trackpad, a lose hinge, clicking sounds that seem to come from the ssd, a loud fan ... Way too loud .. Or is it? , an unevenly light screen, backbleeding, a slow toshiba ssd, a scratched body, broken usb port, flaky wifi connection that switches off when bluetooth is active and disconnects randomly, dead pixels, a bent bezel and of course, last but not least, tiny holes in the screen
8. Do not forget to share your progress with everyone and enjoy