The Rebels premiere features the Wilhelm, which is right and proper.
There was also another noise that caught my ear when I first heard it while watching the Extended Preview clip.
If you go to http://trekcore.com/audio/ and find Computer Beep 10, you'll note that it's the same sound (minus a slight modification) as the sound of Kanan releasing his cargo crates while on the road out of town.
In the Rebels preview, it's at 5:59 or so. While the preview's sound design seemed like it was probably complete, I figured I'd wait till the premiere to confirm that it was indeed in there, and it is.
Nothing wrong with that sort of thing, mind you . . . everyone snatches from Trek's sci-fi sound libraries (I think I've heard both Trek and Wars use one another's weapons sounds from time to time, for instance). Nevertheless, it amused me to have caught it.