2013 Mustang GT problems?

Servus I’ve recently noticed a few things about my car: – Brake Knarzt in front of the stand as when driving. Had made new blocks and liquid a month ago, there was then quiet until today, now it is quiet again… -Rolling speed fluctuates slightly in the stand between 500-600 rpm. I had already disconnected the battery to “learn” the throttle valve after instruction, except that gas pedal has a more direct effect, no change. -If the car is cold Is the first two gears (expanded) very careful to enjoy (the car bucks something) but after 10 min complete Is the normal? Unfortunately I lack a reference to the 5.0 Coyote. That’s why I hope someone can help me here. MfG