[SCOTCH RAT]

i have found 2 of 4. does any one know where they are.

[kero]

I can help with the first and third one. But im sure they are the ones you have.

1. BLIND
Mission: Sierra 117
Only about 1 minute into the game a ship flys over and lands with water in the background. The scull is over to the far right of screen.

YouTube - Halo 3 Silver Skull 1

2. Grunt Birthday party
Mission: Crow's Nest
Probably about 6-8 minutes into the level you go through a half circle metal tunnel. At the end of it you jump down a hole. Before you jump turn around and fall backwords. Push forward when you start to fall and you will land on a ledge. The scull is right up in front.

YouTube - Halo 3 Silver Skull 3

edit: added video found on youtube by holdxtoTrick that helps explain where they are.

[kattahn]

Possible:

I have not read anywhere yet that the last 2 silver skulls have been found...i am thinking 9 gold, one on each mission, and 4 silver, first 2 are on 2 and 4, so 6 and 8 would have silver skulls? Just a hunch, might help to narrow the search a little bit. although im not happy, at all, for a silver skull on 8 h8 that lvl

[Virus]

Thank you =)

[Chazwazer]

The next Silver Skull is the Cowbell Skull.

Cowbell Skull Effect: Explosions become much bigger in the game.

Cowbell Skull Location:

The “Cowbell Skull” is found on the level “The Ark”, and marks the third Silver Skull found in the game. It’s fairly far into the level, so it takes a bit of time to find it.

Begin by heading all the way to the part of the level where you battle the Scarab. After defeating it, look in the middle of the desert area which you battled it in for a fairly large structure (it’s the building you see if you are at the bottom of the ramp you are supposed to go up, and turn to look in the opposite direction). Inside of this structure are several Gravity Lifts (shown below). Take one of these for later.

Next, head up the huge ramp, and head inside of the building (the one with the cartographer inside). Pass through a few of the rooms in this building, and you’ll eventually come to a room with a whole lot of Explosive crates. Right after this room is a Staircase/Hallway that leads to the level below. The Skull is located at the top of the room, at the point where you turn on the staircase to head for the next part of the slope. There are four platforms above you, the Skull is on the uppermost of these platforms. Use the Gravity Lift to jump up to it, and there you have it!
Credit goes to halo3planet.com, thats where I copied it from.