From what I've read it's normal on standards until the car gets up to running temp. That's why you only notice after the car has had time to set and cool down.
Ive been hoping for the valance to come out. Ive been trying to find a take off from someone changing to the 350 valance so i can see if it can be modified fit the base without having to cut the bumper up.
Thud is normal, rattle however ive never heard on mine. Are you letting out of the clutch to soon? If you havent order a clutch spring from steeda asap. make a huge difference.