Silicone tends to absorb odors more readily than other materials. There are a few options that will strip them of that nasty freezer-burn smell. One is to bake your trays in the oven at 350°F. Just make sure the molds can tolerate the heat. Molds or trays with any traces of plastic will melt in the oven. Other options include soaking the ice mold in vinegar or using baking soda to neutralize the odor.