New champion teaser?

I swear I've heard a teaser a few times in the past few days. I can't make out what the noise is, but it sounds like a distorted voiceline/sound effect of some sort. It seems to play randomly in-game as it sometimes gets mostly covered up by ability sound effects and stuff. It's happened around 3 times now. I'll try to grab a sound clip next time I'm playing. Anyone else heard it?
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