Speaker buzz

I'm having a problem with a buzzing sound coming from my driver side tweeter - the one mounted in the A pillar. I bought my base 07 used this spring and every few weeks I'd hear this interference coming out of the driver's side tweeter but it never lasted more than a couple minutes. It's definitely related to the ICE as the frequency of the buzzing matches the engine rpm (alternator whine?). As soon as I take my foot of the gas it stops. Starting last weekend it is no longer intermittent. As long as my foot is on the gas the speaker is buzzing like it's full of bees and it's driving me crazy. Does this sound like some kind of grounding problem?
A little background - I had a VAIS installed about a month after buying the car but it died after 60 days. It's basically an I-Pod charger now. Could this be part of the problem? I seem to remember having the problem before the VAIS installation but I'm not positive. I'll be taking it to the dealership to have this looked at soon and I assume they will try and place all blame on the VAIS unit.
Any thoughts would be appreciated.