One question....
I assume that you're talking about the PBS east on AMC-21??
Reason I ask, is that I just now was trying the other PBS HD channels, ie the Clear Feed HD on AMC1, which worked fine, and then I tried the NET HD channel on G28. The video on the NET channel came in fine, but NO AUDIO ????
I looked at it with TSREADER, and the PMT lists 2 audio streams, PIDs 52 and 53, however 52 is completely missing, and 53 is there, but is flat-lining with no content. Strange, particularly after you've posted about PBS missing audio.
If by chance you WERE referring to the NET channel, I wouldn't be concerned, as there are often problems with that transponder, as I think it's just up there as a filler between sporting events, and I don't think they are very careful about the content. However I really assume you're talking about 12140 on AMC21, and I don't have much of an explanation for that one.