Brand new Macbook pro strange is making a constant metallic 'tink' sound'

Hello I really need some help here. I finally decided to make the jump from Windows to Apple and I'm having the WORST time. I am on my second macbook pro 15 inch (brand new) because the first one had major defects that became noticable within 2 weeks and they had to give me a brand new one because of those defects. My second one (the one I'm having issues with currently) is making a strange metallic 'tink' sound quite often. Sometimes it happens every 10 mins or other times it happens every 30 min. I noticed this from the first day I took it home, and its still happening 2 days later. Could it be the SMS and there is a defect with this one too? I don't think this is a normal because my first one, although it had its problems, did not make this noise, and at the Apple store I didn't notice their mac's making the sound either.

Has anyone experienced this problem?