Quote Originally Posted by VinnieGTP View Post
Check connections like they said.

Even more remote possibility is it's from your cell-phone. What service do you have and is your phone in the car with you when it happens?

Why does my cell phone make my computer speakers emit noise? - Yahoo! Answers
I am sorry I just don't think that is a possibility, this is usually a hardly audible buzz when associated with this problem the subs probably aren't even capable of playing that buzzing noise as it is in such a high frequency range.