I have HotRod cams and a 3650, when im sitting in idle it chatters just like in the posted video's, it goes away when the clutch is depressed but does not chatter when driving at all.
I did not have this problem at first after the cam install, my tuner has the idle set at Ford's spec of 680 RPM, with a hand held i lowered it to the lowest allowed setting 560 RPM, thats when i first noticed the chatter. It seems once the car warms up and really hits the low idle point at a light is when im hearing it. When i was playing witht he idle going upwards of 700 RPM would get rid of the chatter, but the idle sounds so sexy at 560 RPM that i just deal with the chatter.
I have not tried swapping to RP ATF but i doubt it will help, so..