One experience will cause an emotional reaction in you. Mostly people talk about when something causes negative emotions. For instance, they might see, smell, feel, touch, taste, hear or experience something that causes them fear, anxiety, panic, etc. This is what it means to be triggered. You feel a powerful emotional response based on past experience. So you most definitley are being triggered by the sound.
However, you don't necessarily have the same reaction to all triggers. Your most common reaction I assume is to switch/dissociate. That's just your response to the trigger. That's all a trigger is: an emotional response to something happening in your life. There is no behaviour attached, meaning that emotion may cause any behaviour in any person. It only connects to the emotional reaction, not your body's response to the emotion.

Example
the smell of perfume ---- triggers ----- fear in someone
The sound of a slamming door ---- triggers ---- panic in another person
A thunderstorm ---- triggers ----- feeling unsafe

The fear, panic or unsafe feeling could cause someone to switch. But it could also just get them to avoid those situations, or to want to hide, etc.
Really there is nothing unsafe about the perfume, door or thunderstorm, but if someone has had bad experiences with them, they will automatically cause that emotion in a person, even if it's a completely different day/time/person etc. It's an automatic emotional response.