Perhaps I was mistaken, I don't see it in there now either. Maybe I was making an internal note-to-self to make that improvement. Try the volume, and if that doesn't help, I'd still recommend drill a hole for the buzzer and put in a tiny mesh grill. Alternatively, make an extension for the buzzer and bring it to the front near the driver, it should be only 2 wires.
I, too, looked at the instructions and decided against it for the same reason and also because the $400 oem kit wasn't any better integrated than a third party system for under $50. If I, or more likely my wife, feels the need to have this feature, I'd install a third party system.
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