I have a 5010L and am very satisfied with it.
Today, I had opened up the MyDlink site for my camera and had the browser in the background.  The volume was up to low white noise.  then I heard a "clink" sound.  Sorta like a spring, or a shutter, or even a metal blind being lifted and lightly dropped.  
I listened for a few more minutes to see if it happened again and it did.  But what suprised me was a second later, I heard a distinctive and loud, slightly mechanical male voice say "Signal" or "Chigol".  It was quick and abrupt like a radio that had suddenly been cut off.
I waited again and heard the same thing.  Same sound and voice.  I've timed it now and it seems to happen in roughly 2 to 5 minute intervals.
I switched to another 5010L that I have in the house and hear it there too.  Then, I switched over to a 930L that I have and got the same thing.
I think all the cameras received a firmware update yesterday.
I have no pets, and there is no TV or radio on in the house.  the cameras do not show anyone in the vicinity of the home