There's a a brief snippit of "As Time Goes By" from the film Casablanca (1942) played when Catwoman admits loving Batman and driving off to face Red Claw. That song is now played as an instrumental overture for Warner Bros. Pictures, as seen in their current opening logo.
Bruce Timm said that the end sequence is geared around the explosions, but they were artistically poor, and the animation was redone two to three times. Although he felt the final product was still awful, they ran out of time and had to air it.