I also can hear this noise in my car since I bought it. Do you guys know what is this ? Sounds like an old computer hard disk

 

Could not hear the rattle you referenced in the video. Rattles are extremely hard to locate without obvious visual clues. The nature of a rattle (sometimes) is to travel along other parts until it resonates, sometimes opposite from where it originates. You have quite a challenge if you cannot locate something loose. Look under the seats, under the rear area carpet (where the jack/related is). Sometimes, something will drop down behind those foam inserts (or the like). If you are absolutely sure the inside is secure (use a rubber mallet in and around body panels and such, could it be a trim-clip that dislodged and fell down and rattling inside a panel), then the next is to securely jack-stand the car (all 4 sides) and start hitting/moving everything under the car. Systematic progression is the plan or you'll go over the same thing again and again. Only if the car is SECURELY jackstanded, try starting it up (be careful, the rpm's will skyrocket if your not careful). Also watch out for moving parts and loose clothing, and see if it is in the drivetrain. I do not envy your search, it could be found quickly, or quite the nutt-buster. Good luck!