Is there anything else to insert to tailgate hinge hole to make the tailgate quieter? It's so loud and squeaky when opening and closing..

 

GREASE!!!!!!!!!!!!

 

I'm gonna try some kind of rubber gasket thing...

 

I bought new hinges for Jon's truck and quickly found out that they were not round at the rolled end that inserts into the tailgate which caused them to be sticky and squeek some.
So I clamped some bar stock in the vise and worked them over until they were round again but now they had a little more slop than I liked so I wrapped them with teflon tape. The tailgate is rattle free and is smooth as silk.

Yuo might try the same thing with your hinges if they are out of round like Jon's were.