Take the glovebox out and go for a spin? Having it open may make it easier to pinpoint the location of where its coming from.

Open the glovebox, there is 4 screws along the header. One more on each side towards the front (where it hinges).... You have to pop the plastic pin out of the damper to get to them. Theres also 2 "plug" like pieces that hold the lower kick plate to the bottom of the glove box, just turn them 90 degrees. The box should wiggle out after that. Disconnect the light & flash light harness once you have enough room.
...Thats off the top of my head so forgive me, I cant recall if it was actually 4 or 6 screws on the header of the box...lol

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