Buzzing Sound when accelerating and deaccelerating

I've started to drive our Prius to work while my Acura gets yet another transmission, but I'm noticing a weird buzzing sound coming from the front of the instrument panel. It is a electronic buzz sound with a definite cut off. It doesn't happen right away, but it seems to occur when accelerating or deaccelerating around 20mph. It only goes off for about 1 second but just long enough for me to hear it, but not long enough that I can figure out where it is coming from.

I've talked with my friends and co-workers who have the Prius and all of them look at me like I'm smoking some funny weed. So I'm curious if anyone else had hard or experienced a sound like this.

I've got a 2006 model.