Centurion Nebulus Nimbus in Astérix and the Big Fight. The only time he speaks at a normal volume is an attempt at whispering. The rest of the time, HE IS VERY LOUD. In the original French, his name is Langélus, a type of church bell. And church bells need to be...? That's right, LOUD.
Siren was raised in the Sonic Canyons, where constant ear-splitting noise is a part of everyday life. He's probably never going to adjust properly, all told. Also, he's a police car; do you really want him to be quiet? Alternatively, he may have come up in a raucous, industrial area of Cybertron full of rough-and-tumble bots, where he learned being anything but loud and obnoxious meant you were overlooked or picked on. There's conflicting canon on the matter.
"Marvel What The..." had "Ahearya", where everybody was constantly screaming (justified as all the nukes made everyone nearly deaf).