This sounds like your sound generator. I assume you hear this at the front passenger side of the car at the windshield? If so, take a look at this thread.
My solution as well as many others since it's a common issue, unplug that thing.
I removed my sound generator yesterday since I believed it was responsible for annoying buzzing/vibration in the car which frequently occurs (but doesn't occur in normal mode).
The removal was very easy, and after removing it, I found that it was indeed the source of the problem. So I was pleased to remove it in that regard.
On the other hand, I was very surprised to find just how much the sound generator contributes not only to the volume of sound while driving in sport mode, but the quality and "fun factor" of the overall sound as well. Without the sound generator, the car is just slightly less fun than before.
Still, as others have mentioned, I am getting used to the difference quickly. I will evaluate the car for a week before deciding whether to keep the sound generator out permanently or not. But I probably will leave it out since the car still has a fine muffler sound and since the sound generator is, after all, fakery to begin with.