Can anyone tell me what the best wall covering material is for quieting AC condenser lines that are run through one of my interior walls? I attached 1"x2" fir strips and 3/4" styrofoam panels between them on this wall and then 1/2" sheetrock over that but still get noise when the AC is on. I don't want to build another wall due to the loss of space. Maybe some rigid fiberglass board? Thanks for any help!