I have a good ear for this sort of thing, I guess.

At the very least, we know it wasn't just added in for the SE, since it apparently was there in the 70mm version.

Why would they then take it out for the 35mm mix? I think it was just buried in the mix in favor of emphasizing the dramatic music.

And considering a lot of the carefully-considered directional/spatial effects in the original EMPIRE mixes (which were lost in the later SE versions), it does make sense to me that it would be faint effect, since Luke's back is to the camera, and he's some distance "away" from the audience. It's more realistic from an aural perspective, that way, instead of having a loud sound effect for a character who is exiting the scene.