Possible Source of Godzilla 2014's Roar. What's your guess?

didn't they say that the new roar is actually the old roar from the 1st movie but modified?

I'm not sure.

they must have modified it a lot if it is

It's actually Metal and dried ice. The metal contricts when touched by dry ice, making a screeching sound. And the deep bellow is made from wood/heavy stuff on a polished (marble?) floor.

I've been playing around with the roars and I've managed to separate the center and stereo tracks from each other. In the Stereo track, there's definitely some heavy sheet of something banging on a floor at the beginning and end of the main roar with a "rolling heavy tube" sort of noise happening in between. However, the ending bellow seems to be heavily processed and more difficult to make out. The center track, on the other hand, definitely reveals a metallic groan in the center of it all, indicating the main "SKREE-" has something to do with a metal hinge or scrape.

Nonetheless, we'll probably discover more in the Blu-Ray release. You know, with 5.1 Surround and all.