So has anyone successfully fixed this?
We are now out of warranty and it’s still doing this. The dealership’s attempt at fixing it made it a bit better but it’s not gone. About to try to do it myself but just wondering if anyone else has fixed it themselves?
I found my issue. And fixed it myself the day before GM bought it back for refusing to attempt to fix it.
The bolts the hold the running board bracket on the front passenger side, were never tightened from the factory.
GM UAW employees were probably on their 17th union mandated break and just missed something so minor that could have caused the run board to fall while driving and cause catastrophic damage or kill someone. But hey, at least their asking for 30% pay increase for doing less.
So, if the issue is not the one of the two mentioned in the TSBs (the HVAC line bracket in the firewall loose or the wiper motor bracket motor arm under the cowl loose), then you may check on the issue I had.
Get under the truck directly where the backside of the passenger side front wheel well and the front of the passenger side running board meet. Or follow your passenger side a-pillar all the way down to bottom on the car.
Under there while looking up, you see a black bracket that secured the running board to the frame. The bolts are behind the fender liner. They were all dangling.
The issue was that when you go 80mph or above. The air dampers move the air around the vehicle and pushes air into the fender liner.
The fender liner rattles and hits the loose bolts. The loose bolts, although they are no where near the a-pillar, rattle on metal and transfered the sound all the way up the sheet metal so it sounded like it was a rattle at the a-pillar/sunroof/glovebox area.
I tightened them to spec and rattle was gone. At any speed. Never came back.
Check those bolts.