when my 3d character raisies arms the sides (serratus area) pokes out.

heyooo!

I am not a pro 3d artist but i have an astronaut character in c4d i am autorigging in mixamo.

in tpose everything is ok, but once the arms go up the characters sides poke out. i dont get it.

does anybody know how to fix this? i will try to attach pics.