So i'm leaving for vacation tomorrow and want to make sure everythings okay, i just put on my apexi ws2 3 days ago and now when i drive i hear it hitting something underneath my car, it seems to be somewhere around the catalytic converter, any ideas as to what this is? Or if i could quickly fix it, which i'm sure i can.

Oh and i already tightened all the bolts so i dont know what it could be