Why do the hardwood floors in my home crackle when walked upon?

I purchased a home that had Harris Tarkett natural maple hardwood flooring installed a couple of years ago. This flooring is throughout the living room and hallways. The problem is, most areas crackle and echo throughout the house when you walk on it. It's very loud! The foundation of this home is slab. Do you think maybe it was the adhesive used? Is there anything I can do to remedy this problem? The floors look great, so I do not want to remove it.