Hey all, so I was getting some interior cabin rattling that I was trying to figure out, and it turned out to be a loose windshield cowl cover.
The sound was not so much a rattle but more of a deep knocking/tapping noise once every few seconds, mostly concentrated around the drivers dash. It was difficult to understand because it happened at any speed and any situation randomly, even sometimes feeling like it was coming from my feet.

Somehow the drivers side corner of the windshield cowl cover was not held down properly and bouncing around with the wind and vibration. If you just grab the cowl and wiggle it you can feel it's loose and banging around. For comparison the passenger side of the cowl was on tight and did not move at all. Since the cowl just sits on the cars metal chassis and wiper frames it was banging plastic on metal and reverberating through the interior. I don't really know how the cowl is attached because there is only 1 visible screw on the drivers side and it's not for the cowl, it's for the metal frame of the wipers. I assume the cowl is held on by metal clips underneath and at some point in the cars life they broke or came loose. I didn't take it apart because it required removing the wiper arms entirely and just didn't feel like messing with it.

So what I did was put some felt tape (the felt side of velcro) between the 2 areas of plastic that sits on the metal, and it worked, no more knocking. The felt tape at least is holding it a little tighter and now not allowing the banging of plastic on metal.

Below are pictures for reference, hopefully this helps someone else out!

 

I had the same thing going on with my cowl, loose on the drivers side.
My fix was to use 1" length of double sided 3M automotive 1/2" tape, two pieces stacked, under the cowl by the arrow which allows it to be hidden.

 

Awesome!