2021 GMC Sierra near dash rattle

EmporerM · January 30

I have scoured the forums for this issue. It seems to be common among other truck owners but none of their solutions have proven to me my same cause. I’m hoping to bring some new light to this issue. I am a little late into the game. Just bought a 2021 GMC Sierra AT4. I have the same rattle: so far I have removed the cluster and added rattle prevention to the AC duct. I have firmly secured the hood release pull cord all the way from the inside to the hood latch. This rattle is driving me insane and the dealership (despite have a new vehicle warranty) charges me $150 anytime I bring it to the shop with this issue. They claim its a harness loose but do not know “which” one or “where”. Any solutions would be MUCH appreciated. The coolant reservoir was missing a bolt. After bolting it down with felt washers on both sides, still no rattle solution.

any images/picture to help navigate would be awesome

Edit: I have completely secured the transmission harness. This is not the source of the rattle. It sounds like it’s coming from behind the cluster area. When I had it taken apart I could not recreate the sound. I feel like it has to be in the engine bay somewhere

Edited January 31 by EmporerM
Adding information

kickass audio · January 30

is this when listening to music or just driving? I have a rattle depending on the song that is playing and i found both my front doors were a big source of the rattle so I fixed that by loosening the 2 screws where your hand goes to pull the door closed and pushing the door panel closer to the window and tightening the 2 screws down. i then noticed a smaller rattle sound on the dash where the defrost vent and the heads up display (in my case it's just the little red lights for the collision avoidance system) and tapping on the plastic above the instrument cluster sits fixes the issue for a little. I need to eventually pull the cover off and add some felt tape to it to stop the rattle but it's not that big of a deal for me.

EmporerM · January 30

This rattle only happens when I hit 50MPH and gets worse the faster I drive. Even when the radio is on and I’m at a complete standstill, no rattle. As soon as I hit 47 MPH the rattle begins. At 70 MPH I have to crank my radio up almost 30% up to drown out this noise.

when I get home today I am gonna explore maybe the transmission harness. I’ve seen where there was a GM bulletin put out for it a few years ago

EmporerM · February 6

FOR THE LOVE OF GMC, the rattle has been found and fixed. One of the screws holding the fender well up was missing. The metal clip that sits in the metal bracket got wind on it at higher speeds. Put a piece of tape over the clip and a new screw in it. Wallahhh.. no more rattle. One key point that made me look there was: the rattle went away even at high speeds when it was raining. The weight of the water on the clip and fender well prevented the metal on metal rattle at higher speeds. I’ve got a video of what it sounded like for anyone hunting a sound.