New engine with mystery tick

Put an engine in my 1969C 10 and
when we picked it up we heard a tick
and the shop told us it was the piston
in the fuel pump took it back in the
spring and said I don’t like the tick
you need to fix it they tore the top
end of the engine down found where
on the cam and put it back together
still checked then in three weeks we
brought it back and they tore the
whole engine down and rebuilt it
under warranty put it back together
and itStill ticked.  Brought it home
and on other mechanics advice we
swap the fuel pump still ticked any
suggestions out there