He said as soon as he saw the actuator move it started to rattle.
This is my take on it/the design.
If the wastegate flap/penny is anything like other turbo and the same as a TD05-18G subaru turbo I have rebuilt, the penny is actually floating/loose on the end of the armateur and not hard mounted/welded.
On an older actuator system the diaphragm pushes the rod outwards opening the wastegate. But it requires several psi of pressure to start doing this. By the time the car generates that pressure any noise generated by the flap rattling is lost in other ambient noises. Or no rattle against its seating position occurs as it moves from rest to open in a faster motion.
The motor driven actuator obviously starts opening the flap slightly/very early in the boost generation process. Hence there is a small window where the penny rattles either against its rest point due to tension being released or as it opens and can be heard due to the low rpm having lower ambient noise levels.