qwedie - Previous response was 100% correct. The odd numbered rooms face south (toward the Plaza) and the even numbered rooms face the freeway where there is continual traffic noise all night long. If you end up in one of these, you need to turn the A/C on fan and the fan will run continuously, drowning out some of the traffic sounds. On the S side, the lowest numbers 01, 03, 05, etc are closest to Main Street and furthest from the train tracks. There are train noises a couple of times each night, which we always get used to after the first night and never hear them again.
One other tip - for a nice view (from the upper floors) go out the exit door at the end of the hallway by the 01 end of the hall for a cool look down toward the Stratosphere and the strip. Don't do this if you have a fear of heights, however.
If you go back through the old posts, you'll find several discussions and descriptions of MSS.
Roy