SX is the base model car. It comes with no power steering, manual tranny, no power anything, or a/c along with a SOHC engine.
Yes the options of your car will effect belt length. However the belt would not effect the tensioner rattle
Remove the tensioner and make sure the bolt that you turn to release tension on the belt is fully seated. Sometimes it can come loose if you turn the bolt the wrong way when removing/putting on the belt and cuase the pulley to rattle. Otherwise you need a new tensioner bc the bearing is bad. $60 IIRC at the dealer.
Replace/fix it before it breaks and you have bigger issues
