The disks get scratched like that if you move the 360 while the 360 is running and the disk is still in there. That's happen to me twice. First for Guitar Hero II and again for Rock Band

EDIT:It could also be the paper slip that Disk 4 was packaged in. I just started Disk 4 but I don't have any problems with mine so far.

Got the same problem, disk 4 of LO doesn't play.

LOL.  My 360 makes loud, wierd noises all the time.

Did you move your 360 while playing the game? That's most likely the cause as the disk tray is slightly bigger than the actual disk, enabling it to move causing the laser the make a circle like scratch on the disk

i guess im one of the lucky ones,this never happened to me...did you buy LO used?

I would make sure your 360 is not on something that moves (like something that vibrates from a speaker, or a table that wobbles when a door is shut).

If the disk is spinning full speed, and the 360 moves slightly, it will scratch the disk in a fashion that you have described. I lose a Gears DVD that way (bumped the coffee table that the 360 was sitting on).

Four possible solutions.

1. Use a can of compressed air to spray out the disc tray. Follow the instructions.
2. Fully power down your console unplug and leave unplugged for a few minutes.
3. When you start the game switch the audio track for the game then switch back. 4. Flip the discs back to three then reinsert disc four. Then quickly save game.

The compressed air can blow out any dust screwing with the laser simple enough, and you should always have a can for your high end electronics anyway. To deal with dust buildup.

Powering down the console is not simply a gag. Powering the console down should help to clear conflicting data out of the systems memory. Until you fully power down your console by unplugging it the data can just lie there. Screwing with you.

The last two issues involve region coding. The 360 contains regions specific data for every region. The region coding on disc four may be faulty. Which means its trying to run a different region then the consoles setting. Flipping the disc could reestablish the correct region coding, or the flipping of the language track can do the same.

Anyway you should try these four options. The last three are easy enough to do, and will cost you nothing. They are all basically software resolutions. The forth is one you should be considering regardless. High end hardware needs to be periodically cleaned anyway.

Sounds like it's the DVD drive. If it's a Hitachi-LG model, then the magnetic spindle has fallen off and the drive arm is searching for it that's why, if I am correct, you hear a urrr, urrr, urrr, Disc is unplayable error. Torx 10 bits and 15 mins should do the trick if is a Hitachi. Put the spindle inside the circular piece on top of the drive and put the 360 back 2gether. It will create a seamless drive then.

Happened to my Gears disc too.

I remember people reporting problem with disc #4 of LO when the game first came out. Probably due to Microsoft cheap ass, packing the game disc into a paper sleeve instead of buying a proper 4 disc packaging. Sometimes I truly do not understand Microsoft, especially the ED division. They seems to be penny wise, pound foolish. Another example is the crappy packaging for Halo 3 Special Edition.

Most other company package a full case inside the steel box or used steelbook for their exclusive. Microsoft seems to love to skimp when it come to packaging. And they don't seems to learn. Sometimes it suck when the company decision get dictate so much by the bean counter.