Noise coming from engine the moment I release emergency brake

Picked up my new 2011 Mazda 3 today. I noticed that when the car is in park and the emergency brake is up, the car is nice and quiet. The moment I take the emergency brake off, there is a subtle hum coming from the engine. When I turn the wheel left and right, it changes the pitch of the hum. It makes this noise regardless of whether the car is in drive or park- its the moment I take the emergency brake off is when the hum starts. It's not loud (but I can definitely hear it) and to be honest I'm not worried about it- the car rides great and has just under 200 miles on it. I just thought maybe someone here could give some input as to what it may be. I'm going to give it two-three weeks and if it does not go away/ease up I'm going to stop by my dealer.

My first guess is that it is a normal noise produced by the electric-powered hydraulic pump for the power steering system. The system comes under more load when you turn the wheel, hence the change in pitch.

I am not sure, but it would make sense the pump is shut-down when the parking brake is on, in much the same way that daytime running lights shut-off when the parking brake is applied.