I noticed something interesting over the weekend. I have two DCS-942L's in the garage that were on wifi and had the exact same noise on the audio. I got tired of the video cutting out intermittently--the wifi has to go through three thick walls, and 2.4 GHz is very congested in my area--so I ran Ethernet cable to them and turned off the wireless. The static seems to have gone away on both cameras.
Also, the 5-6 second lag before an event shows up on the video stream is also gone.
Try connecting your camera with wired Ethernet and turn off the wireless function in the camera setup.