Audio develops static after 40 mins

I bought a WD TV Live Plus, set it up and updated the firmware.  Everything was working perfectly, but about 40 minutes into watching a movie the audio developed static (like a radio station silghtly out of range).  Pausing/resuming did not fix it.  Turning the unit off and resuming the video did fix it temporarily.  This happened to everything I watched or listened to (always about 40 minutes into it), so I thought maybe the unit was defective and exchanged it.  The new unit does exactly the same thing (with un-updated firmware).  I swapped out the HDMI cable with the one from my Blu-ray player (which does not have this problem) but that did not solve it either.  I also tried a different HDMI input on the TV to no avail.

I have not found any other threads here about this problem, so I’m a bit worried.  Please help!

Update: Pausing the movie, unplugging the HDMI cable from the back of the unit and plugging it back in does fix it temporarily, then the problem recurs after ~40 mins.

The problem seems to be limited to HDMI.  I am using component/audio cables instead without problems.  I suppose that will have to do.