Weird rattling sound under/behind the dash?

[Kris@modmynav]

Hello,

I've noticed rattling sound under/behind the front upper dash (seems like behind of air vent) today,
it doesn't rattle all the time but once I hit bump or rough surface road, it comes up.
I couldn't locate where it comes from, so I checked glove box, behind of Nav unit and cluster box to see if there is any loosen wires or something,
but nothing worked, nothing was loosen.
basically it starts when I my LEFT FRONT WHEEL hits bump or rough surface first.
does someone have any idea?

Thank you for your help