Gasoline pump *solved*

So, it's done. Sound away!!

It was actually the pressure regulator ! I ran the engine today with a hose right on the pressure regulator... and there was nothing.
And when I wanted to take off the feed line on the injection manifold pipe despite "pressure loss" (run the engine and BP fuse out), there was still a huge pressure on it.
I then did the same on the parallel vehicle, and here at the hose history immediately came gasoline from the return flow on the pressure rod and also the feed line was not so under pressure during dismantling.....
So pressure regulator installed by the parallel vehicle with me, and the noise is/was gone.
This brings an odyssey to an end again; and despite the anger, man has learned a lot again... Thanks to all who stood by me with advice and action.

PS: Tank cover is defective; but was known, therefore the open tank cover for the whole test series.