Why did a piano start playing during my onslaught?

So I am in the middle of Capture the leader match on Gridlock, with bullets flying, and chainsaws out... Suddenly piano started playing... It is extremely dramatic playing too. Why did this piano all of sudden start or what triggered it? Is it only on this map the piano plays on?? Did something trigger it? It might be the same tune during a specific moment in the single player campaign ( but I could be wrong)

Solution 1:

http://au.ign.com/videos/2011/09/22/gears-of-war-3-easter-egg-secret-song-mad-world-on-gridlock-hd

That video explains it but basically, if you finish a round without killing any of the ash people it plays the song, "Mad World", an amazing song that was in the original trailer. :D