So new update.
When the codes cleard, they did mit come back. Today i worked with the mechanic at the car. When we start it, there was the creepy noise again. When we took of the hose from the IAC Valve, we mentioned, that there sucked Air in but also Air comes out. It's like bubbling. Hard to describe.
At first we thought that the catalyst were clogged. So we sepperated them from the exhaust mainfold. Same Problem.
So we put everything together again.
now we suspect a defective intake valve, because when the engine gets warmer, the noise comes directly.
Tomorrow my mechanic want to unscrew the valve cover and do a pressure test.