Viewsonic n3251W: sound problems in some channels

[raubvogel]

I've had one of those TVs here for quite a few years. Since last Saturday it began to show the following problem:

o On some channels I have no sound whatsoever. I want to say they are the ones we watch the most but cannot say if that is related.

o On Saturday, one of the other channels were showing all the shows with sound track in Spanish. But, all commercials in English. Yesterday it went back to all English.

I had the Cox maintenance guy here and he said he could not find any issues on the signal... at least not with the gear he had. Could that then be on the TV? I have no problem getting sound from its hdmi and RCA ports. The flowchart in the repair manual only accounts for no sound whatsoever from the tv circuit, not my situation.