My former Chief was a retired L.A.P.D. detective Sgt. He told me that those old "Growler" sirens would "Growl" when the cars were on the freeway at freeway speeds. To combat this annoyance, at the beginning of the shift the officer's would take the prior days "Hot sheet", fold it up and jam it into the grate over the stator. This would stop the sound from bugging the officers. You had to remember what you did before you turned on the siren, otherwise the siren became a large confetti machine and the brass took a dim view of police cars spreading confetti. Just trivia, Gents!