Recommendations on sound dampening material
We just installed the new Rheem heat pump in our house. The blower is located in the closet at the first floor and the closet door with the air intake grille faces the hallway, so we have some noise which we try to lower to the minimum. Contractor who installed Rheem lowered the blower speed 10% (that helped) and sealed all small holes, but we still hear sound of the blowing air from the top of the unit and from duct that connects directly to it.
As a last remedy, contractor recommended blocking of the upper half of the closet door grille, approximately 23x42 inches, with a sound dampening material. The lower half will remain open and this will be sufficient for air intake. A brief experiment with blocking the upper grille with a cardboard indeed reduced the noise level.
As a sound dampening material, contractor recommended an "insulation shield", half-inch or three-quarter inches thick. The stuff with this name I found in Lowes has a foil on one side and some paper on another. In my opinion, it will not dump sound but just reflect it inwards.
Is it the right thing? Or there are other sound dampening materials that we can attach to the grille from the inside? Perhaps something like a blanket made of soft material that absorb sound might work the best. Any recommendations would be greatly appreciated.