New to the forum but thought someone may be interested in a fix for the passenger side rattle - I've seen on a lot of other forums where people have been having the same problem.
My Zetec-S is 7 months old now and a couple of months back it developed a really loud annoying rattle from the passenger side. I couldn't work out where it was coming from at all - it was either the passenger door, back passenger side (where the fourth door would be), or the boot. I spent hours trying to find it, even took it back to Ford but they were useless.
Anyway, this morning I've spent another hour on it and have finally found it! If you take the trim off that surrounds the front seatbelts (it's held on by flimsy clips so be careful as I nearly snapped them) once you have one clip off slide your hand behind the trim and gently pull away from the car and the rest should unclip enough so that you can see the whole seatbelt casing. Right at the bottom of the seatbelt casing (to the right hand side) there is a plastic 'arm' that is feeding a wire through. This is banging against the metal and causing a rattling sound when driving. All I used was a couple of double sided sticky foam pads to secure it in place and now have no rattle
!! I started to get the rattle on the driver side as well so have done the same