Sound travels really easily on a harp and almost any noise any place on the instrument will sound like it’s coming from the action. So it’s probably coming from the pedestal with the F pedal hitting something. Does the sound happen when you move the pedal sideways(out of the natural slot) or when you move it up and down? You might try laying the harp down on the floor and moving the F pedal with your hand while you look up into the pedestal to see what is hitting. If you can locate the source of the noise I can probably tell you what you have to do to stop it.