When the Sound Transit Central Link LRT opened in 2009 there were a number of complaints about noise. Measurements showed that the noise levels were substantially higher than expected. ATS was part of a team who investigated the source of the high noise level and provided Sound Transit with specific recommendations for reducing noise levels. The high noise levels were found to have been caused by a combination of inappropriate rail grinding that left the rail head substantially rougher than necessary and non-optimized wheel and rail profiles. ATS performed detailed measurements of noise and various rail parameters to diagnose and resolve the noise problems.