One reaction I ALWAYS have, and can't seem to control, is if a car backfires (or similar noise) I will jump backwards and on the ground, in a crouched position – my girlfriend at the time thought it was weird and she still brought it up again well after . … I still get startled by revving motorbikes and sirens on emergency vehicles. … I do not think it is a unusual or particularly a trait for people on the spectrum although people on the spectrum have it a lot more intensely. …

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Fear of sudden loud noises? – General Autism Discussion