Engine knock and whine are two highly undesirable parameters which many times are exhibited as amplitude modulated signals. Overall quality, cost and timing targets demanded that engine assemblies exhibiting knock and/or whine be screened out before they reach final inspection in their respective motorcycle frames. This required production line QC systems which could quickly and reliably test steady state and time-varying parameters in a production environment. This paper describes a computer networked based system that utilized a real-time 1/3 octave analyzer. The described system was part of a successful program to control and improve the sound quality of Harley-Davidson engines.