I had FIOS installed a couple of weeks ago. I have no problem with 3 of our STB's, but with the DVR I have a couple of problems with the sound.
First, on recorded video the sound level is very low - have to crank the volume up very high just to listen.
Second - when watching TV I get a distinct audible 'pop' every time I change channels. I hear the pop occasionally when playing a recorded program also, like when the program ends.
I'm just running the sound through our TV speakers, no home theater etc.