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I have the same exact noise in the video above on my 2020 Denali 6.2L, although I would not call it a squeak or a chirp, more like a metallic rattle or tinking (say -- ball bearings in a ceramic coffee mug). It goes away about 10-15 seconds after starting up cold, or as soon as I put it in gear. I can also hear it come and go quickly when auto-stop restarts the engine back up. And most annoying to me, I can hear it when cruising down the road and accelerating with light throttle, just as you described. With more aggressive throttle it does not happen. All of these characteristics make me think it's definitely tied to engine load or associated vibrations, and could be related to something loose, something that twists, or even the exhaust. I have yet to crawl under the truck to poke around, but the first place I want to look is at the exhaust system, exhaust shields, flappers, etc. One time last week I heard it with the door open, and gave the truck a gentle rev. That made the noise go away, but not before I could hear it change and seem to be coming from under the truck. Granted, being parked on concrete that could have been coming from anywhere but it really seemed to be traveling from under the truck to my ears. Pretty sure it's not anything serious but it is just enough to annoy me.

Comparably equipped, there was only $3K difference between SLT and Denali when I shopped. For the extra $3K the Denali includes some features you can only get with added packages on the SLT (like X31) and some features you cannot get on the SLT (adaptive suspension, power running boards, etc). Many of these differences are subtle and many customers probably don't realize it. I suspect if you were able to put a proper value on all of this, it would account for most of that $3K difference. The rest probably goes to the chrome, etc. Personally, I like the look of SLT over Denali. But I could not find an SLT equipped with the features I wanted. Denalis included all of those features, and more. So I bought a Denali. I have to say, the adaptive suspension is a huge improvement over the stock suspension. I like the power running boards (do not like having fixed running boards hanging down all the time). The rest of it I could take or leave. If you can find a Denali without the Ultimate package, compare the pricing and features to an SLT. That is probably the closest in terms of a match, and may be the easiest way to compare the two.

Read the chart. Compare 4WD to 4WD and there is 440# difference between the 5.3L and 6.2L models. It also translates into a reduction in the payload and trailering number for the 6.2L. This should not be new to anyone, it's been like this forever.

Look at this document here and scroll to the bottom: https://media.gmc.com/content/media/us/en/gmc/vehicles/sierra-denali/2020/_jcr_content/iconrow/textfile/file.res/2020 GMC Sierra Denali 1500 Product Guide.pdf There is 440# difference between 5.3L and 6.2L Denalis and that extra curb weight directly subtracts from payload. I don't think it is all related to the engine weight but somewhere along the line the 6.2L Denali is carrying an extra 440#.

The 5.3L is about 440# lighter than the 6.2L, so that is a good place to save weight. 2021 Interior will not be all-new, just something related to the center console.

Likely that's where the relay is.

If it shuts down in park that would also explain why the sound went away when I stopped in a church parking lot to listen. So it's sounding more and more like maybe this was a regen.

Well, the dealer had it idling for 15 minutes before I drove it, and I know that is not good for the DPF. And it had been taken on a long test drive overnight by another customer, and no telling what they did (the HVAC settings were all out of whack and I can just picture somebody's cold wife sitting in the passenger seat complaining). So it's very possible it was due for a regen at just 100 miles. That could have been it. I probably only drove it for 15 minutes altogether, and it may have been in regen the whole time. Would there be an indicator on the dash when an auto regen happens? I am extremely familiar with regens on Tier-IV tractors, and it can be a pain in the butt. I end up avoiding idle and keeping RPMs up during operation, and that helps avoid manual regens or inconvenient regens. I hope the truck is less finicky.

Definitely not a normal turbo noise. The whistling on acceleration was an additional louder, lower frequency, and fluctuating noise on top of the normal turbo whistle. I thought the turbo whistle was very subdued and refined, and just perfect. This other noise sounded wrong and out of character with everything else.

About how often does this engine do a regen? The truck had about 100 miles on it from test drives.

I test drove a 2020 Sierra SLT with the 3.0 diesel, and loved the engine. Would have bought the truck but it made an annoying whistle noise on hard acceleration. Almost like the noise a windshield leak would make, but directly tied to my right foot on the accelerator. I tried revving the engine while in park and the noise did not happen, so it seems like it's tied to either load on the engine, airflow over the vehicle, or maybe motion of the drivetrain. HVAC on/off made no difference. Anybody run into this before? I did a search and have seen a few older threads about whistle noises, but they didn't seem to correlate to a 2020 diesel (production in early March). It's sort of funny, I was enjoying the faint turbo whistle (very familiar with that sound) thinking how quiet and refined the engine is while cruising, then this other whistle blared out at me whenever I dipped into the throttle. I could even control it by getting on/off the throttle. Fascinating to think about, but no way I would buy the truck like that. The salesman said he'd have a dealer tech look at it, but I am not optimistic they really care enough to dig into it.