Ed is having problems where the volume in his Vizio soundbar changes audio as he changes the channel. Leo says it sounds like the IR from the Verizon FIOS box is merging the two commands and passing a volume command to the soundbar. There are only so many IR codes, so it's possible the confusion is causing it.
From the chatroom - Here's a technote from Tom's Guide that says this is a known issue with the Verizon set-top box. He will need an update from Verizon to fix it. Until then, there is a workaround. Change to stereo from surround. From the chatroom, it seems this is a known issue. Verizon apparently has an update you can get from them. There is also a workaround by changing the audio settings from surround, to stereo.