I have an bungalow which was extended about 15 years ago. At the "join" of the original building to the extension a crack is present - it may have been there a long time and the surveyor did say no structual defects are present. However, i've recently become more aware of the crack as I can feel it under the carpet. When rolling the carpet back, tapping the concrete floor sounds hollow - as if there is a 1-1.5 foot wide trench running the length of the boundary of the old and new part of the building.
Just wondering what that could be?