Run sounds played at constant pitch

With possible future rubber tyre routes it would be useful to simulate the “sshh” sound of the tyres on the rollways such as on the Paris and Mexico City metros. However, openBVE run sounds rise in pitch as the train accelerated faster. Would it potentially be possible to keep the pitch of the run sounds constant while the train changes speed? I have seen some instances where this is done by attaching to the motor sound but this is a problem when you stop applying traction or brake.