Many dogs scratch their crates to make them as comfortable as possible. Also, this could be a way for a dog to mark his territory. Furthermore, dogs might scratch their beds to make them more safe - in this way, they are checking whether there is anything inside their bed that might bother them during the sleep. Also, a dog might scratch his crate to make it more warm for him. This is also perfectly normal and you have nothing to worry about if your dog scratches his crate for these reasons. However, a dog might also scratch his bed due to anxiety. If you determine this is the cause, you should try to figure out what is causing your dog to become anxious.