Welcome to my world. I am also a new v360 user with an LG TV.
You probably want to look at a post I made a few days ago. It contains a list of faults that I hit in a 6 week period, as well as a solution to all of them. Well, all bar the softish Sky Sports HD picture that seems to be a generic issue for most viewers.
I am sorry to say the workaroud is a hardware solution, designed to avoid the TV handshaking directly with the v360 box via its hdmi connection. But it does work and will probably save you a lot of future pain if you have only found the volume issue so far.
I don't know how to link to posts within the forum but here's the title...
"LG TVs and Virgin 360 woes - a solution or at least a workaround"
The volume buttons didn't start working properly until about an hour after the intermediate box went in. They are still working correctly 5 days later.