i can definitely see it being a vacuum

They have stated multiple times that they digitally modified the original roar till they got the roar that they have now.

A quote from the Godzilla Art of Destruction book on how they created his roar:

"Eventually I found the best sound was metal friction- resonating metal with dried ice. Dried ice supercools certain types of metal, and it starts contracting and vibrating and produces this shrieking and bellowing. That became the central design elemant for the updated Godzilla roar."

There's also something in there about how moving frniture on a waxed floor created the low "OONK" of Godzilla's roar. 

^Interesting. I thought it was a modified version of the original.

@SciFiKing 

Nope. C: However, they did try the Glove on the Double Bass method, but they couldn't create the same feeling as the original.  

^Very true.  They even worked with original Toho recordings, studying them and working to make an updated version.  With all the fuss they've made about saying "its a secret!", I'm skeptical of the G:AoD explanation... but that certainly sounds like a likely way of making that incredible roar.  We may never know... ;)

Ahhh yes, I thought Im the only one who wants to know, but yes, it maybe a vacumn, BUT one of the clips showed their recording of a fighter jet taking off, supposedly it's one of the sounds hidden in the roar, I played with one scene of the roar and I can definitely hear a jet, but i wanna know what else is hidden within it.

@TohoGfan55

They were recording the jets taking off for the sounds of the jet s in the movie.