My house is built on a concrete slab in low lying marsh land. After a few days of decent rain a sour, cheesy smell permeates one half of the house. The drains, wall cavities and ceiling space have been checked and all is well there. I have been told that pockets can form under the concrete slab but how do I check this and what can be done if this is the case? The smell will usually go away after some good drying weather but in the mean time everyone is left feeling sick from the stench. I do not believe this is a mould problem as the smell is sour and there is no evidence on damp spots on the tile flooring. I recently pulled up the tikles in the kitchen and the cement looked fine. However, cement was poured on top of an existing slab when the garage was converted into a living area. Hope this makes sense and someone out there can help me find the cause and solution to this revolting problem. Thanks in advance.