shockvalue

Just installed a Swann ADW 350 wireless security system which has a camera and 7" display. The picture is OK but the audio is abysmal. Both live monitoring and recorded playback has static or crackling in the audio. There is also a constant hiss. I have tried all manner of trouble shooting to try and eliminate this( different power source, location etc) but the crackly sound stays. Swann tech help have not been much help. If there was some sort of electrical interference I would expect the picture to be affected also. Not sure whether I have a faulty unit or whether these things just have crappy sound. Any other owners of this system or similar setups have the same experience?