The series' opening music starts with drums and lightly mixes in the Star Wars theme. Why is that an homage? The 4th draft of the original Star Wars was written by Lucas starting with war drums.

The 4th draft is essentially the first real version of the saga that we know, it's the first one that begins with the "A long time ago in a galaxy far, far away", and it's largely the one that was crafted into the shooting script, the first one with help from Gloria Katz & Willard Huyck...
[FONT=Times New Roman]The Adventures of Luke Starkiller
as taken from the "Journal of the Whills"

[/FONT][FONT=Times New Roman] FADE IN...[/FONT]
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A long, long time ago in a galaxy far, far away
an incredible adventure took place...[/FONT]
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FADE OUT...[/FONT]
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FADE IN[/FONT]
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1. EXT. SPACE[/FONT]
[FONT=Times New Roman]A vast sea of stars serves as the backdrop for the MAIN TITLE. War drums echo through the heavens, as a ROLLUP slowly crawls into infinity...[/FONT]
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[/FONT][FONT=Times New Roman]It is a period of civil wars in the galaxy. A brave alliance of underground freedom fighters has challenged the tyranny and oppression of the awesome GALACTIC EMPIRE.[/FONT][FONT=Times New Roman]
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[FONT=Times New Roman]Striking from a fortress hidden among the billion stars of the galaxy, rebel spaceships have won their first victory in a battle with the powerful Imperial starfleet. The EMPIRE fears that another defeat could bring a thousand more solar systems into the rebellion, and Imperial control over the galaxy would be lost forever.[/FONT][FONT=Times New Roman]
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[FONT=Times New Roman]To crush the rebellion once and for all, the EMPIRE is constructing a sinister new battle station. Powerful enough to destroy an entire planet, its completion spells certain doom for the champions of freedom.[/FONT]
As you can see, while the final script still was still looming on the horizon, this was after Lucas all but started over and what we know as Star Wars really came into focus. And that idea of "war drums echoing through the heavens" was dropped in favor of John Williams excellent opening theme, but clearly it had a place in Lucas' mind, and now enjoys one in Star Wars: The Clone Wars.

So love it or hate it, now you know where it comes from.