Sound drops out from ND5XS

Hello all,

Yesterday I had my ND5XS playing in the background, and I heard the track stop mid song.  A few seconds later it came back, and then it did the same thing several times.  I thought maybe there was something wrong with the file it was playing, so selected a different album.  There was then no sound at all from anything I selected.

I then switched from Upnp to iradio.  The sound was there, then it wasn't!  No sound at all from any input.

I powered down the ND5, waited a minute or two, then powered up again.  Still no sound.  Then I rebooted my NAS, (Synology DS211j), and tried again.  No joy there either.  I then powered both down and started up again.  Still no luck.

I left it for an hour or so, and then for some unknown reason I decided to turn off my ethernet switch and the ND5.  Left it off for a minute or two then powered up switch then the ND5.  The sound was back.  For the rest of the evening all was fine.

After coming home from work this evening, I switched to iradio.  Once again no sound.  I changed the radio station...no sound.  I switched to Upnp...no sound!  I left it a little while, and then came back and selected some music through the Synology Audio Station ipod app.  This time music played for two and a bit tracks and then loss of sound again.

I've had the ND5 for about five months now and it's never done this before.  When the sound goes the track is still playing according to the display on the front, but there is no sound.  All connections are wired to an independent ethernet switch, which is wired to a Netgear router.

There has been no change in set up, nothing has been moved or unplugged.  I'll have to contact my dealer I guess, but has anyone else experienced a similar problem?

Is it, (as most network problems seem to be), an ip address conflict?  If so, should I use a fixed ip address, and if so, how would I set this up?

Help!