MuuMuu101's 68 Dart, A Learning Process...
So I now also have a T56 Magnum, Centerforce Dual Friction (which was also on my 4-speed) and a hydraulic throwout bearing. I find that also if my car is idling (approx 950 rpm idle speed) with the engine warm that mine also rattles. Its totally silent when I drive down the road, clutch released or not, and also it goes away if I push the clutch down. I believe also that this is a transmission rattle of the countershaft gears and the mainshaft gears moving back and fourth on each other - which is not cushioned enough by ATF in order to be silent. I have maybe 85 miles on it so far and it's done this the entire time.
I'm not particularly worried. My 2004 Chevy Colorado has an Aisin AR5 transmission which makes similar noises in the same situation but is a bit quieter - and has over 118k really hard miles on it. When I changed the fluid, it was amazingly clean - but it runs 80W-90 GL4.
I plan on dropping the Dexron III in the T56 Magnum after 500 miles (so that will be sometime in 2019 due to the weather in Michigan) but I don't expect to find an issue.