When walking through a house that is about 10 years old, I'm hearing an intermittent crunching sound as I walk across the floorboards. This is different to the creaking sound that I hear in some older places.
What can be causing the crunching sound, should I be concerned about the sound?
The floorboards are placed directly on a concrete slab.
What steps can I take to identify if this is a concern?
It is possible, even likely, given the recent date of construction, that the concrete slab was topped by a leveling material. These leveling materials can be either self-leveling (very liquid-y) or hand-applied (more like mortar or thin-set consistency) and are used to both level the underlying concrete floor slab and to fill cracks, depressions and other imperfections prior to the finished floor, such as tile, carpet, vinyl, wood, etc., being installed.
It is also possible that this leveling material has degraded and cracked due to any number of other factors ranging from continued slab movement to improper preparation or installation of the leveling material. Because it becomes hard when it cures, if it has cracked apart, it could easily make a "crunching" sound below your wood floor.
Another possibility is that an adhesive, if one was used to bond the wood to the concrete (if not a "floating installation") could itself have degraded and/or come loose from the substrate (either the concrete slab or the leveling material) or the wood itself.
Finally, I might wonder about termites. The little devils are very good at damaging wood components while leaving no trace on the exterior surface.
