I also have the clicking noise under hard acceleration that you guys are describing.
I went through everything just as you did and cannot find a source.

I actually have come back to it may be belt skip. I have a chassis brace, new belt, new gears and a CA glued clicker.

I decided I am just going to run it til something breaks or strips.
I have been doing this for 5 to 6 race nights and nothing has shown itself. It also has not gotten worse. I expected it to get worse over time but it only happens on the same 2 places on our track and is very predictable.

It is always just after exit of a hard right turn. I am thinking it may be twist in the chassis allowing the belt to slack?

Our layout changes this week so I will see if it keeps happening and where.