I'm currently trying to reproduce the sounds of Elton John's Song for Guy as a learning project, and I'm stuck with the wind-like sound that accompanies each chorus (and the third and following repetitions of the initial song motif at the end, before EJ starts to sing).

I have a quite convincing bass, and the strings that accompanies the second part of the chorus to its conclusion are good too, but I can't understand what that sound is. I've tried some white noise with a low-pass filter (with a slight resonance) where an envelope changes the cut-off frequency of the filter along with the chorus' parts and it sounds like it when the frequency is high and the sounds morphs into a kind of hiss. However, when the frequency is lower, this isn't it, and by long. It sounds like some king of chord, but without tonality, only resonance, if you get my clumsy meaning. But what chord, anyway, as it seems to be always in tone with each part of the chorus (or it's the filter doing that)?

How on earth is that sound made?

PS: In addition, I found that my accompaniment lacks depth. As a relative newbie, I added more reverb, but that's not enough, obviously. Is there resources on the web on how to construct studio "wall of sound like" depth? And how one teaches oneself to recreate sounds (I've watched hours of sound design videos, but I'm often stuck when trying to learn how to make a sound from a song that is not exactly what I found in some tutorial)?