My grand daughter is 5 moths old...sometimes you can hear her knee or other joints click or crack..is this normal because her bones are soft + growing?

Probably normal: I would not worry too much about it it is probably a normal situation.

It's OK: Babies have very elastic ligaments crossing over the joints. I tell parents to think of them as very stretchy rubber bands. As they move, the ligaments stretch and snap just like a flexible rubber band would, and you hear that clicking or snapping noise. It is totally normal and nothing to worry about.