Audio problem: When Vader is talking to an Imperial officer in the hangar in the Death Star, when the officer says, "It must be a decoy, sir. Several of the escape pods have been jettisoned." his head is shown from behind, but his profile shows his mouth is moving before the words are heard. (01:03:55)
Audio problem: When Vader and Tarkin learn that Leia has lied about the location of the Rebel base, we hear Darth say "I told you she would never consciously betray the rebellion." There is a pause and Vader continues to move. An obvious dubbing error.
Audio problem: Widescreen version: When Tarkin attempts to make Leia reveal the location of the Rebel base, he says, "You would prefer another target? A military target? Then name the system." In the next shot, his head is shown from behind, but the motion of his jaw shows that he is still talking, even though nothing is heard. (00:56:00)
Audio problem: [Special Edition only] In the scene where Luke and Leia swings across the missing bridge, a number of the shots fired by Leia are "bangs" instead of the laser "zap" sound. The bang is probably from the prop gun used (it shot blanks) and was never dubbed over (until the 2004 DVD release).