rattle sounds either like a loose baffle plate or maybe the cats breaking up depending where the rattle is coming from exactly. Power cable should come into the car on the passenger side behind the fuse box which is located behind the glove box
. hard to reach but i used a metal coat hanger to drag it down carefully from behind the fuse box without removing it. 
PS does the rattle stop when the clutch is pushed down ?
PS does the rattle stop when the clutch is pushed down ?