Weird vacuum/hum sound?

Okay bear with me, because this is probably going to sound ridiculous. Every once in a while (maybe every couple days), I hear this medium-high pitched almost vacuum like sound. The closest thing that I can relate it to is the noise that the monster makes in Lost, minus the clicking.

I know about the West Seattle hum, it's not that. I'm in Wedgwood. But also heard it at my best friends house in Burien. She noticed it too and has never figured out what it is and I swear anyone else I ask tells me it's an airplane. But there's no way.

It usually lasts for a couple seconds and never happens more than once, with at least hours in between each time I hear it. Any thoughts? I've tried to get a video of before but it's so quick.