I am getting the whomp whomp noise coming from my front end left side needle bearing on my 2020 TRD ORP with 24K mi and goes away when 4WD in engaged. My last 4R did the same thing and it was a 2011 SR5, dealer ended up replacing the entire front differential and this got rid of the noise.
So I already complained at 5K and 18K mi and dealer said this is normal, I know there was a TSB on this a few years back but not after 2018. What concerns me is nothing has changed on my 2020 to remedy the issue. Vehicle is still under warranty, what should I do ? I know East Coast Gear makes a bushing to repair the issue but will end up costing me $500 or more to fix something Toyota should take care of for free. I could drop off and tell them to fix it and call me when the noise is gone.

If the dealer says it is normal - ask them to come along in a test drive of a new, on the lot 4 runner. When that does not make the noise ask them which is normal. If they say it is normal - drive another new one.....repeat....

Any suspension mods?

No mods, totally stock.

There is indeed a TSB that includes 2020 model year and newer for this issue. There are two repair procedures depending on the model year shown in the TSB. For 2020, the TSB calls for the diff to be replaced which would include an updated mount that is threaded to allow for a dynamic damper to be bolted to it.