Thank you very much Mike!
I have created a new project. And I have also checked the mixer and the c/d DIR was set only on 1, i have set to 0 and its gone! This tiny little number ;-). Everything’s now OK!
Only if i put in the headphones, the C-Input-Chanel-LED is lighting green for a little while, but i think thats no sign for something bad?
Have a nice evening!
Best, Alex