273 auto trying to find the 'tick'

There are a lot of places where a tick noise can come from. The flap in the right manifold is one of them. Exhaust gas pressure constantly changes from one bank to the other.
This thread reminds me of a episode of Andy Griffin. The entire car was disassembled and put back together inside the court house because the owner wasn't happy with it.
A "tick" is not a knock. Good hunting though.