Can somebody tell me what Underlayment is best for Laminate floors.  The underlayment suggested was about a dollar a square foot.  They said it would greatly cut down on the hollow tapping sound.  He said I need at least 6 mm.  Is thicker better? Can I use 3 mm and double it? Is there a best material such as foam, rubber, cork Etc.? Is there any other inexpensive or creative tricks or alternatives to keeping the floor quiet?