Are you 100% sure that nothing else is causing this issue meaning any loose things inside the door pockets etc? Reason I ask is coz it happened with me and it was just something of mine touching the vehicles body on uneven surfaces.
Secondly, don't take this issue lightly. Please take the car to the dealership ASAP and don't wait for the 1000 checkup and re create the sound which the car makes and ask them to fix it.
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