Little Plug/Jack, 1" long ?

I am in the SAME BOAT, although I bought an M17x R3.  I called tech support just to find out what it was and they could not find an answer.  The woman on the phone told me to take a picture of it and email it, but I just didn't bother.

But I have the same exact question, WHAT IS THAT THING?!

It sounds like a S/PDIF adapter. If it is, then it would be connected to the jack right next to the MIC input jack. Page 16 in the manual states that an adapter is shipped with the computer. I don't personally own a M18x, but that is what your descriptions sound like when I compared it to the manual. Hope this clear things up.

DO NOT USE THIS. It will mess up your on-board sound. I messed mine up just by plugging it in. If you have already and lost your on-board speakers realize that nothing is wrong with the speakers. The S/PDIF adapter will bend a pin inside the hole that tricks the motherboard into thinking S/PDIF is on all the time. You can get your mobo replaced but that's a pain. You can also bend the pin back with a tiny metal hook if you can find one. I personally wouldn't risk that though. I've only had my M18x for 3 weeks now and i'm sure its still an issue as it was an issue for people back in January. Unfortunately Alienware knows and still refuses to omit the S/PDIF adapter even though it causes issues. In order to fix the issue if you don't want to replace the mobo or bend the pin is to uninstall the IDT sound driver and allow windows to install their own driver. After that your on-board sound will come back. Once again, its not an issue with your speakers and don't let Alienware assume that it is until you attempt the uninstall. Just a friendly warning! The S/PDIF port is the fourth port on the left, if your facing the left side of the laptop!

I wish I had waited for Isendar's post, now my computer is messed up, 2 months old and I have to try to get them to repair/replace it, They don't make it easy to get to them either.

Fumming! Mad!

Phew!!   Thanks for the info!  Glad I never messed with it!  Once I get my system set back up (its boxed) (flood-victim) I am going to look for that piece in the box and THROW IT AWAY.

OK I found out what that little plug is for, still not going to use it. I got lucky, after a system restore to 10/22/2011, everything apears to be back to normal. The plug I was told is an adapter for a fiber optic connection, as I said I am not using it, don't have fiber optic cable to connect to, wouldn't attempt without documentation in hand as to proper placement and use of the adapter.

Neill048 - That's almost correct. This fibre optic cable your referring to is better known as S/PDIF or a digital/optical connection. It does use fibre optic to transmit high definition sound data between a reciever and a source. If you had a 5.1 home theatre sound system you could theoretically connect the S/PDIF port to the laptop and the laptop would transmit 5.1 surround sound through the reciever. Problem with the M17x/18x series is that the port pins do not reset once the S/PDIF adapter is inserted into the port. This in return fools the motherboard and drivers into thinking that something is always plugged into the S/PDIF port causing a whole slew of other issues. Your issue may not have been as severe as mine and some others and maybe only caused by a software glitch. I'm glad you were able to resolve your problem. I have found a pseudo fix for my issue and will be cancelling my M18x return due to other reasons (Dell makes you get antivirus now if u want to purchase the laptop)!