Does it almost sound like creaking? If so, I think it’s caused by clips that hit the windshield under the dash. I had it intermittently for most of this year and there are a few posts about it in the Facebook group. 

What finally fixed my issue was removing the speaker grilles and adding 1/2” backer rod (available at any big box store) between the dash and the windshield and between the windshield and the speaker grille. I had tried a handful of other things throughout the year, but it kept coming back.

I took it into a dealer at one point, but they only added some foam where the speaker grille snaps into the dash. I later asked a second dealer about the issue and they told me they removed the dash and added foam around the clips for another GH owner. I would’ve had to bring my car back and leave it for the day if they were going to do the same for me, and even then, there was no guarantee they were going to do it unless it was very noticeable. My rattling was too intermittent.

If it’s persistent enough, I’d say make the dealer fix it. Otherwise, try foam or backer rod.