Wind turbine (WT) sound annoys some people even though the sound levels are relative low compared to other man made sources. A reason for this could be due to the amplitude modulated sound – “swish and thump”. Measurements of sound immission from WTs were carried out continuously 1 year at two sites in Sweden. A method for quantifying the degree and strength of amplitude modulation (AM) is presented. AM is strongly coupled to the weather conditions. AM is observed at our two sites approximately 20 – 30 % of the operational time depending on the distance from the turbines. Continuous acoustic measurements were taken for one year at two different wind turbine sites in Sweden. The sites were covered by forest; one site is relatively flat while the other has shifting terrain. Meteorological parameters from the ground to above 120 m height were measured in parallel with the acoustics. The long measurement time capture all different sound propagation conditions that occur due to seasonal and daily variations in the weather.