In 1999 three types of two-layer porous asphalt pavement were built in Øster Søgade, a city street in Copenhagen, with a section of dense asphalt concrete as a reference. Since then the pavements have been monitored. The initial 6 - 7 dB noise reduction compared with the noise level at the reference section has vanished over the years due to gradual clogging of the pavement pores. After 8 years of service, the drainage asphalt was worn and ravelling had begun. The Copenhagen municipality decided to mill away the top-layer and replace it with new porous asphalt. Noise measurements were carried out in 2007 as part of the European project SILENCE, before and after replacing the top-layer. At two of the test sections most of the initial noise reduction had been regained, while this was not the case at the thinnest pavement (with 55 mm total thickness while the others were 70 mm and 90 mm thick, respectively).