My husband and I are building a new house and our installing a washer and dryer on the second floor. We are concerned about the noise level on the first floor and want to soundproof the floor. We are building the home ourselves and are look for an inexpensive, effective way to do this.
I too, just built a house, I wasn't worried about sound on the floor below just the sound getting through the walls. I insulated all the walls. They were internal walls but I was doing it for noise, not heat loss. It seems effective. I also did this to the master bedroom and all bathrooms. Nothing worse than hearing somebody tinkle...or worse. I am sure there are sales people out there who have a magic product for you to buy.
I don't think you could go wrong just packing fiberglass batt insulation into your floor joist space. However some sound/vibration will still travel through the joist itself.