All sorts of possibilities. You didn't say what type Verizon box, TV, and what type of connections.
- Check the audio settings on the stb/dvr. I recommend setting it to FIXED volume. This leaves your TV to control the volume instead.
- If only some channels, you may be trying to send dolby digital signals to a box that doesn't support them. In that case you need to get in the hidden menu and make sure you set LPCM only. For Motorola boxes, from on, hit the power (off) button on the box, then hit ok and menu button on the remote. Timing is sometimes tricky but if you do it right you will see one of the hidden menus (user settings). Down to additional hdmi settings and hit enter, Down to audio output and hit enter until you see L-PCM. Turn off and then on.
- Check tv's settings (obviously varies by make)