Mine does this even if the ac is off and does it with remote start and also when pressing the start button in the cab with the AC off, so the compressor would not be kicking in when using the start button. If the ac compressor made a noise this loud that can be heard from that far away, I would definitely take it to the dealer for replacement as that wouldnt be normal.
If I could just reproduce the issue on demand, I bet they could find the problem. The noise mine makes is not normal. The dealership was unable to reproduce the issue, and we went for a short drive yesterday to see if that would induce the noise. it never made the noise for them. I drove it back from the dealership near work to have lunch, (about 20 miles) and when I started it after having lunch (20 mins later) it clunked very loudly.

 

Guys did you read ^this^ maybe he's onto something?

 

The AC compressor will engage anytime there is airflow directed to the windshield to dry the air and keep it from condensing on the windshield, even if your AC is turned off. Sounds like the compressor clutch to me. They hit pretty hard when the engine is first started, as the RPMs are quite high compared to a normal idle ( 1200-1500 at first start vs. 600-700 at warm idle). The compressor goes from dead stop to 1200rpm when the clutch engages. It'll clunk.

 

For the a.c. compressor to kick in, the air control has to be on in some form,defrost etc. In my case, the fan is off, the a.c. is off and it is not in defrost mode. When the a.c. is on and the clunk happens, the clutch can be heard and seen to engage well afte the clunk has happened. Even the dealership that did hear the clunk said it was not the a.c. compressor. They said it was the wastegate, but I highly doubt that.

 

I disabled auto start stop with forscan tool. The clunk can also happen after having sat overnight or a few days.
my current theory is that it's somehow induced by suspension travel or road bumps. Someting is getting jarred or moved to cause the noise. I'll know more tomorrow.

 

I have the same issue since the day I got the 2017 3.5 eb with 4x4.

Once the engine warms up and you will hear this clunk sound when you start the engine again.

This is definitely no ac, alternator whatever people have guessed. It's more of an engine mechanical / transmission related!

I am going to check other new 2017 3.5 eb on dealership lot for this sound!

 

interesting note today, but let me state this first. Everytime we park the truck, with the foot brake applied and the transmission in neutral, we apply the parking brake, release the foot brake and allow the truck to rest on the parking brake. Then we place the truck in park. This morning, when the wife went to start the truck, I was watching the rear ujoint near the differential, and the drive shaft ROTATED a little when the truck started!
It didnt rotate alot, maybe a half inch, but some. This seems extremely odd to me as I have never seen an automatic transmission cause the drive shaft to move when a car is started. If the shaft is being moved when the engine is started, that would explain why the sound is so loud sometimes and seems to come from the entire bottom of the truck.

I also modified one of the videos I made so that it repeats the clunk sound to make it easier to hear.

 

Yep, something is causing the driveshaft to try to turn during engine start. I should have filmed it and i didnt but after driving to a local restaurant for dinner, when I came out, i pointed my phone light at the rear differential, and i remote started it. There was a loud bang, and the driveshaft attempted to turn really hard and bounced back fairly hard. It reminded me of the movies when the bad guy gets his necked snapped, there was a quick attemp to twist and the driveshaft snapped back to its original position. I will try to film it tomorrow. I think i may also have figured out how to reproduce the issue too. I still need to do more attempts, but I think this is how to do it:
Drive the truck normally. When drive is completed, stop the truck in the desired parking spot, but do not put in Park. With your foot holding down the brake pedal, put transmission in Neutral. With your foot still on the brake pedal, engage the parking brake. The truck should still be in Neutral. Now rev the engine about 4 or 5 times so it jumps between 2500 and 3000 rpm. Then place the transmission in Park. Shut off the truck. In both of my tests, the truck was off at least 20 mins, but I'm not sure that matters yet.

 

Started the truck about a half hour after last info post here. I recorded a video this time. Its fairly easy to see the driveshaft moving back and forth.

 

Of course the driveshaft is going to turn till the parking paws engage.. When you park the truck first put it in park let them engage and then apply the parking brake.