I sealed my front and back doors with storm doors. They cut the sound dramatically while helping with the insulation. Mine are these from Larson:
Shop LARSON 36"W White Secure Elegance Fixed Glass Only Storm Door at Lowes.com
My garage entry door also had huge gaps. I ended up insulating the garage door with these:
Corning Garage Door Insulation They get mixed reviews at Amazon, but work well for me.
Since the garage enters into my utility room, I weatherstripped the utility room door and it helps a little. Then I put a floormat at the foot of the door to further seal the utility room. The sound from the washer/dryer is cut considerably.
I also installed double-cell cellular blinds on all my windows that seem to help a lot.