As rare as it is for me to agree with McGrath, the Death Watch Beetle
                                  is a good possibility. The species mentioned, Xestobium rufovillosum,
                                  is European. The term comes from the beetles tendency to make a
                                  "ticking" sound when they bore through wood. The beetle is quite small,
                                  approx. 3/16 of an inch (or 5mm), usually less. The sound is very faint,
                                  hence the name. The sound was not noticed until late at night when
                                  ambient noise was very low.

                                  Several closely related families such as Bostrichidae, Lyctidae (Powder
                                  Post Beetles), and Psoidae all make some noise when actively chewing
                                  in/on wood and can also be considered suspects. Do you have firewood
                                  stored inside? If so, listen in the vicinity of the wood or move it to an outside
                                  storage area and see if the sound stops.