hmm the hinges are probably damaged from an impact or poor treatment. ideally you can get to them through the bottom of the laptop. you could try using some silicone spray (mind the motherboard, that stuff is all slippery and could make a mess) but based on the sharp creak, there could be a bend in the hing system. see what apple wants for repair. I have dealt with apple a\many times, and I have to say, they will never just do something without your consent. I brought a macbook with what I knew to be either a damaged motherboard or HDD ( someone had stepped on it while it was open) and I was unable to verify whether the board was just toast, or the hard drive was the issue, as it would boot, but never load the OS. They managed to get it into diagnostic mode ( refused to launch for me) through their magic Ethernet cable thing and verified that it was the HDD. this did not cost me anything other than 30 minutes, and when they told me it was the drive and I told them I would fix it they did not push that they do it. long story short, they will tell you what is the issue for free, and they will only repair it if you tell them to.