When the Blue (Whiteish) light came on you could hear the same roller coaster chains when the monster grabbed Locke. Those same chain/pulley noises came on when the light came on and Kate started screaming. If thats the case Desmond has control over the monster? Or is it even a monster at all and not just a chain/pulley system?

I guess I should clarifiy something. The sound is the same sound in the Season 1 finale when Locke was being drug accross the ground and Jack was trying to save him. The same thing trying to pull him down the hole.

Listened very carefuly. The music emulates the chain sound. It's not the same sound as the chain that pulled Locke.