I to like Del B. also have a clunking noise every 4,5,or 6th start ups. dealer has no clue as to what it ism no surprise there.
Del B? Are you referring to a recent Best of Car Talk podcast? Suggest to provide some more info: engine/transmission configuration and explain w/more detail
- What part of the car does this sound seem to be coming from?
- When? Under what conditions? Driving down the road? During engine cranking? Shifting from P to D? P to R? etc …
Del B. left a poor description of the problem. “Startup” could mean starting the engine or could mean pulling away from a stop. With only 1500 miles on the vehicle, this sounds like Del doesn’t like the way his new truck shifts.
Do you have the 6 speed or 8 speed automatic???
And how many miles are on it???
The 8L45 (8 speed) (and 8L90) transmission had a rough beginning. You may need to find a good late model transmission builder that knows how to repair, not just rebuild them…
I think they might have had some TCM issues as well…
We have a lot of Canyons in our fleet in that model year range and some of them have those same symptoms 
There have been a few Chevy Canyons with perplexing problems been discussed here in the past. OP might want to look through those posts using the forum search feature, link upper right this page.