I'm noticing something strange lately.
Was watching Mad Men on Netflix, which is in 5.1 and a few episodes had the centre channel dialogue all muffled. Couldn't tell if the centre was off completely, and maybe the muffled dialogue was whatever was supposed to be coming from the L/R speakers. If I switched to 2.0 it sounded fine. I figured it was a Netflix problem. And it wasn't every episode.
This morning I noticed certain commercials were cutting out the centre channel. One would have no dialogue, and then the next commercial would be fine. When this happens, sometimes my Yamaha amp would make the 'click' sound it does when I change audio channels or turn it off/on.
The Netflix and TV audio come from two different components.