Sound Waves + Closed Box --> What happens under movement? Setup:
We have a closed, and from the outside isolated, box with two sound-emitting-generators placed at opposing ends, and one microphone placed in the middle (--> picture).

The sensors are all placed in such a way that the microphone does not pick up any noise, as long as the box is in its initial state [total noise cancellation through sound-wave peak and valley annihilation]. 
Moreover, let's assume the medium of the box is simply air for now.
Question:
If we move the box, will the microphone pick up any noise/sound?
My Thoughts:


*

*One the one hand, the relative position between the noise-emitting sensors and the microphone is not changing at any point throughout the movement. Thus, the wave-constellation does not change (?), and thus the microphone should pick up no noise.

*On the other hand, the movement should move the bounding-walls closer towards an already before-the-movement-started-emitted wave which should let this wave then create a different echo-effect than without movement. This would most likely change the wave-constellation and destroy the perfect noise-cancelling, and thus, the microphone should pick up noise.


Please help me determine which thought of mine (or none) is correct :S
 A: By Galilean invariance a box moving at constant velocity and a box at rest are indistinguishable from inside the box. In that case, the microphone should not pick any "noise".
The analysis is more involved if and when the box accelerates. A simple way of accounting for acceleration is to consider a box at rest under the influence of a horizontal gravitational field. Say the box is accelerating rightwards and pseudo-gravity is then directed to the left. In that case, air will have higher density near the left edge and lower density near the right edge kind of like what happens in earth's atmosphere. It seems however that sound speed does not depend much on air's density and is much more sensitive to variations in temperature. In any case, if the acceleration is large enough and/or the box large enough and/or the microphone sensitive enough, then it should pick up some noise.
A: If (1) is correct then the air moves with the box (let's say is not air, is a solid), as it seems to assume that the air remains at rest relative to the box. If the air moves with the box then the front waves will instantly add a movement in the same direction of the box, thus (2) is false. 
