Okay, I just had something weird happen.
I did most of the Fallow Mires things with a party I never had together (VIv, Bull and Cole) and I had banter! Twice in the hour and a half I was in there. Combat sounds were there as well (I heard Cole yell something), no combat music though, except for the Avvar fight at the end. But other music happened.
Journal and codex were cleaned up.
Then I went to the Western Approach, had music. Did some exploring (no banter, with background music), before I entered the Tevinter Ruin in the north. Had people comment on stuff (rarely happens), no banter, no combat music, except for the fight at the end. That might be intentional though.
After I exited the ruin and finished up that part of the Western Approach, things quieted down. No sounds in combat, except for the usual atmospheric sounds. No banter and no music. Maybe it is surpressed for that area, but I don't really know.
I kept my journal clean throughout, fiddled with audio settings, but I didn't get banter back.
At least the temporary fixes work on occasion. I know that banter twice in an hour and a half is not a lot, but it's something. Cannot really place the banter in terms of where it is supposed to happen, because it was so generic (Bull asking Viv about her favorite type of magic, and Cole asking Viv about whether she feels spirits when casting magic), so it might have been from anywhere.