Oh you're right, that is creepy, but cool! My main sim is a vampire and I have never heard that sound, which is good because it wouldn't suit him - he's more your 'friendly neighbourhood vampire' type. He also has the undead aura (tier 1) and eternal sadness weaknesses, so it definitely isn't linked to those. Also if your alien is doing the same thing and neither are hybrids then I doubt any of them are linked. Grim isn't the daddy is he? :D It sure sounds similar. Perhaps it could be mods/CC related, a hidden trait or just a random glitch. Does it still happen if you start an entirely new save? I'm really intrigued!
