Buzzing sound while car is turned off...

[Duckydos]

OK, I have posted this question before, and didn't really get an answer. Well, I tried to forget about it, but it really bugs the hell out of me.

Here's the deal, after my car is parked and turned off, it makes a weird buzzing noise, almost like a little motor turning. It usually occurs once after I turn the car off (for like 3 seconds or so, then it tapers off) and then at random after that. The car can be parked for an hour, a day, even a week, and it will still make that noise occasionally. Even last night, my brother and my dad were talking outside and heard the car make the noise (it's been parked for over a week).

Anyway have any idea what it could be?

-Ducky