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I've baited the traps with chocolate, cheese, nuts and peanut butter and put them at various points along the carpet and beside cupboard of the bedroom wall which I think they run through the skirting board of (does that make sense?) It is the front wall of the house.
I wondered about the plumbing, but believe me over the weeks I have learn't to differentiate between the various noises the house makes. The central heating clicks on at 5.30am and the scrabbling is well before that!
As we live in a terrace, I think that they may use our house as a run to get from one side of the terrace to the other.Don't get me wrong the neighbours are very house proud! I've never found anything gnawed or eaten, even down in the kitchen. It is as if they just run through, in the skirting boards - I presume that there may be gaps in the brickwork behind the skirting boards.
Thanks for many & varied suggestions :o)