Check your cover for the cabin air filter is seated properly. I insulated that whole HVAC system under the "hood" on mine with foil backed closed cell foam sheet. I also put some heavy butyl rubber on the inside of that cover because it is right above the engine.I have noticed that there is a little more engine noise in the cab when I open the air intake in the centre of the dash. No ac or clever stuff in my van, 1999 model.
Here is an example of one that isn't seated properly: