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.

In our kitchen remodel, I tried my best to minimize sound from the upstairs shower. I bought the "soundboard" from Home Depot (I think it's about $7 or 8 for a 4x8 sheet) and baffled it into the soffit area. I also put in pieces of drywall, as I've heard its density stops some sound penetration. I even used some styrofoam insulation.

I even expected sound to be deadened some more after I'd put in cabinets, etc. But for all the effort, I'd say that the sound reduction was noticeable--but not by much.

As hoganem says, some sound just travels through the framing. You sometimes hear that common walls between condos (and the like) may be built with an airspace to lessen noise.

In our case, I'd say our efforts weren't worth the trouble. But I wonder if you might be able to build up some kind of subfloor under the appliances? Raise them up a few inches?

I think there are also metal pans you can put under the washer, in case (somewhere down the road) a leak develops. Might be worth a look while you're at it.

Good luck,
-k2 in CO