2014 Avalon Hybrid Engine Ping/Knock Sound

UPDATE: It wasn't loud enough after warmup for Toyota to do anything about it. After driving a quiet Camry hybrid for 10 years, I just couldn't get over the noise from this engine. Car is gone and now I drive a Lexus SC430 with a smoooth V8.
Conditions
Outside temperature: 76 deg F
Engine warmup: Engine running for 7 minutes; Temp needle near middle.
I'm dealing with a pinging / diesel type sound in my 2014 Avalon Hybrid that has been present since I purchased it Certified Pre Owned in 2017 with 36K miles (50K miles now). Listen for the dull pinging noise (lower pitch than the rest of the sound you hear).
I'm revving the engine here so you can hear the sound come and go. Inside the cabin, the sound proofing cuts out most of the normal engine noise, except for this pinging sound. I would not be bothered if the sound only existed outside of the car.
Temperature is 76 deg F and car was running for 7 minutes right before the video, so not a cold start. A lot of the noises are healthy Toyota engine clatter, but it's the diesel knock type sound that has been bothering me. I had been (barely) living with it, until I test drove a 2014 Camry Hybrid with 75K miles (mine only has 50K now). The Camry engine just hummed and buzzed nicely, right from startup. It is very clear to me now that my engine isn't "right".
In winter, the sound is very prominent while accelerating until the engine is fully heat soaked (15-20 minutes or more). On very cold days with a lot of stop and go (car in EV mode frequently), I have to deal with this noise through most of my commute to work.
After fully heated up, the sound is subtle and intermittent. In the summer, it is also present, but noise is about 70% compared to Winter. Sound seems loudest around 2100 RPM.
NOTES:
* For the first 5 seconds after it first starts up in the morning, the noise is not present. After 5-10 seconds, I hear the knock noise start to appear.
* Worst noise is when I am accelerating up a moderate incline 8 minutes from the house in cold weather. Passengers always ask what the noise is and if the engine is failing.

[@zim777]

Did you ever determine what the issue was? I have a similar noise now when it’s cold

[@aromaticpillow]

I never found out exactly what it was. Some guy on a forum with symptoms like mine alluded to it being related to EGR on his car, requiring engine replacement in the end (I assume the EGR issue caused some damage). Unfortunately for me, he got the new engine free from Toyota after some settlement/agreement and removed his past posts on the issue,. I never got to learn anything more.