I don't know the answer but I can imagine underfloor dampness causing this - particularly as you mention the heavy rain and marshland.
If your house has suspended woden floors damp may have come up through the gaps in the boards and wetted the underside of the carpet. The moisture would be trapped between the underside of the carpet and the top surface of the floorboards.
As the external environment dries out and things get warmer the dampness remains trapped under the carpet causing the bubbling even in a hot summer.
I think you need to lift part of the affected carpet and look underneath.
Good luck...
Peccavi
July 2009
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