Oddly, I did not recall this problem happening when I first hooked mine up. Once it started happening, I noticed happening on all digital channels. It seemed to be happening during the primetime network shows that I am assuming each had a DD 5.1 soundtrack. I, however, had low audio and sometimes but not always had no dialog. Commercials, syndicated shows before and after my shows (presumably with a 2.0 soundtrack were fine). Commercials during my shows were fine but when the show came back, low audio. There was no other rhyme or reason to it other than it started happening on all channels.
As an example I had recorded the first 3 episodes of DRIVE on Fox and first noticed this problem after recording the 4th (and last). At first I thought it was the Fox broadcast, as I never had a problem with ABC but then ABC started doing this. I then confirmed the problem on my CBS shows. I can't test NBC and the only CW show I have recorded with it was 1 episode of Everybody Hates Chris and it was fine (DD 5.1 soundtrack?)
This weekend I found where to turn off VSS and the live audio coming thru the tuner lept to life with a richer, fuller, more vibrant sound and wider soundstage. I have only been able to record ABC last night with good results but still far to early to tell if that was isolated or if the problem is gone. Now that I have turned off DST and have my timer recording more reliably, I have been experiencing frequent U99 errors all week.
I must admit Panasonic should have done a better job field testing. The only reason I have been willing to put up with it this long is the good reception, PQ and recording quality.