It's the Deflector's (a Minigun from Mann vs. Machine) sound for the Brass Beast.
Before you say "all you did was rename files": Bug off. The Deflector originally had no Critsound and no "empty" sound. I also had to fix up the spin-up because of the Brass Beast taking longer.
This video shows the "better" empty sound, which I included in the zipfile also:
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