I know what you mean about not wanting the dealer to touch your truck but you might as well give in and let them have a go at it.

 

mine had a rattle the first 4000km then all the sudden stopped. i say let it be for a bit see what happens

 

It's under warranty, take it in to get it looked at. I had issues with my passenger door and it took a few visits but they did a good job nailing it. Lots of things can go wrong on the assembly line and they're more focussed on production than quality at that stage. That's why there's a warranty.

 

Did you ever find the source of the rattling? Mine has been squeaking/rattling for some time now and after removing the door panel 5 times, applying duct tape to all loose plastic parts, I still cant find the source. Takes me 30 seconds to remove the panel now I've gotten so good at it. The noise seems to be coming from the area near the seat belt height adjuster. Not sure if the dealership would be able to fix this without driving a lot so I don't want to waste my time bringing it there and having them troubleshoot. I'm so frustrated I'm about to inject some expandable foam in there to see if that helps.

Update: Searched other threads and found this one:

http://coloradofans.com/forums/114-...rado-forum-2015-gmc-canyon-forum/215465-squeak-chirp-sound-cab-ext-z71-4x4.html

Going to poke around the headliner and floor sill tomorrow to see if that solves it. Never thought of that because I'm convinced it's coming from the door itself.

 

Mine does this, but its only when I'm listening to music with a bit of bass to it. I've thought about just using sound deadening material on everything in there.