John,
While my Sundance had air flow at all the vents, the volume at the bedroom vents was very low. I pulled down the interior trim for the bedroom roof vent and discovered that the AC ducts on both sides were open (probably prep for front AC) and leaking into the ceiling cavity. I sealed these and it helped. I also found that the AC itself was not well sealed in and around where the AC met the ducts. I sealed around there too and it also helped. But, the biggest difference was the TimK sheet metal mod. That helped quiet a bit. Give it a try.