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I got in touch with apple, and after many conversations on the phone, where they asked me to send photos of the charger, the serial number and the plug of the mac, I finally go to the appointment at the Apple store. The guy at the Genius Bar says that it's normal for the material that the macbook it's made of and he doesn't notice anything in the 20 minutes we were there together. He also said that the Apple store was not the best place to check such episodes, considering that the floor and every aspect of the store it's made of materials that do not create such problems. So after a chat with his colleagues he came back and decided not to keep it for further investigation. He also made some general checks and everything was ok. I guess I'm also getting used to it and noticing it less and less.
 
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