Is there any special meaning or occasion associated with the song?
I noticed that as soon as most of the guests had left along with Edmure and his bride for the bedding ceremony, the gates were closed and the band began playing a different tune which happens to be the Rains of Castamere. As soon as the band started playing it, there was a sudden look of dread on Catelyn's face. IMO that set the gears in her mind in motion and she started to put together that this was a trap.
So am beginning to assume theres some background involved with song. Is there?