Beyond the standard noise terms (shot, series and 1/f noise), in some cases microstrip sensors are affected by other noise sources, which can be recognized by their odd time (or frequency) dependence. One source of additional noise is the continuity of resistive layers surrounding the strips, e.g. p-spray on the n-side of a double sided sensor or electron accumulation layer on the p-side. Another one is the thermal noise induced by p-stops to n-side strips. The results obtained on a set of double-sided silicon microstrip detectors showing these excess noises will be presented. The static measurements which can foresee such effects will also be discussed. The seminar will start with a brief overview of the activities on silicon sensors, fabricated in the clean room of FBK (Trento).