Aly,
In most cases the problem with voice quality has little to do with the gateway and more to do with your network. Since you are using the DX, no noise, static and such, would be caused by the DX directly. Now if you are connecting the E1 to some type of channel bank or GSM device, it is more likely the noise is from there. Dead air could be a config problem, not dialing the number correctly or a network problem.
MikeM
mike_voip@hotmail.com