Hinges weakened on MBP 13"

It seems that the hinges on my 3-month old MBP have weakened, though I can't be too sure. Once opened, the screen stands freely which isn't a problem. When I close the laptop and have it at 90 degrees the lid opens a centimetre or so if I don't have a hold on it. I can't even be sure whether this happened before or not...any ideas?

Would this be covered under warranty?

Cheers