When the X-Wings were about to descend towards the Death Star's surface, the rebel music theme was muted. Did anyone esle experienced this?

Boy, you need to learn your past and present tense.

It has allways been like this. That's supposed to increase the tension.
You can see the same during the lightsaber fights, or when Obi-Wan chases Jango through the asteroid field. It makes you concentrate more on the scene and what's happening there. The sound effects make the music.

Fans Discover Glitch in 'Star Wars' DVD Soundtrack

Fans of John Williams are up in arms over an apparent glitch in the new Star Wars DVD set in which the left and right channels fed to the rear speakers in surround sound are reversed in the original Star Wars movie (Episode 4). John Takis, who frequently analyzes film scores for Internet groups, points out that the violins can be heard coming from the left surround-sound speakers and the cellos from the left. "It is essentially a 124-minute audio glitch," Takis writes on the John Williams fansite, [url]www.JW-Music.net.[/url] "The sound effects are correctly positioned in the surround channels. It's just the music that's backwards." Takis also takes issue with other aspects of the sound mix for the original movie. "Remember the awesome fanfare version of the Force theme that kicks off the Death Star battle?" he writes "Good luck hearing it this time around -- it's virtually inaudible."

Day one of release - Lucasfilm commented on this and said it is NOT a glitch.

Or they're covering for their mistake.

Or you are over analyzing the movie...

For pete's sake, Jovan, no one on these forums is overanalysing the Star Wars movies, they're discussing them...because these are "Star Wars discussion forums!"

We come here to talk about this stuff, not to have you tell us we shouldn't...so chill out.

I heard the music? It's just drowned out by the radio comms and the laser effects (the radio makes the atmosphere more than the music, imo.).