Missing helicopter sounds on any map

Hello, recently I've noticed that there are no sounds on helicopter NPCs on any map, can someone fix that if possible? That happens with Synergy Vanilla and a clean installation of Half Life 2 with episodes [It happens without episodes too, doesn't make a difference]

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I don't know if the console error messages are related, this issue occurs on dev branches too unfortunately, I've tried to verify game cache and reinstalling half life 2 and synergy by deleting their folders from my Steam game folder without luck, I've noticed that it happens on different computers as well.

Hoping to get an answer!