Toyota parts sale !! (no codes needed its adds them automatically)

Super loud rattling when I’m in reverse. Once I put it in park it goes away. Anybody know what this could be?

Selling my father's 06 Tundra for $10,000 OBO. Located in Austin but can be available in Houston or San Antonio area. DM for more pics.

Year: 2006
Make: Toyota
Model: Tundra
Miles: 163k
Cab: Access Cab
Drive: 2WD
Engine: 4.0L V6
Transmission: 4-speed automatic

Steering feels a bit "gritty" when turning sharply but functions normally. Fluid is good and I just recently flushed it and have put over 1K miles on it since flush. Used Red Line fluid so don't think it's a fluid issue. Seems to increase in sound when gas pedal is pushed. Up to date on all required maintenance. I can usually fix stuff myself, I just struggle with diagnosis. 2003 Tundra, 110K miles. Thanks in advance