This sounds very similar to the problem I'm seeing with my hauppauge PVR-350 card.
I noticed that when I set up some analog channels in "services" under the TV adapters section (including the proper frequencies in Hz) when I afterwards preview an anlog channel with "play" under "Channels" section I get static in the vlc window.
I also see that at the time i select "play" that v4l-ctrl -F reports the analog frequency of the tuner was reset (by tvheadend I suppose) to 44Mhz which is the lowest frequency the card supports, as if it is reset instead of set to the proper frequency.
If I set the frequency manually using v4l2-ctl -f 792.0 (note: frequency is specified in MHz, not Hz contrary to services frequency field!)
vlc starts showing the proper video+audio!