The very good news is that as far as his development is concerned, he is bang on schedule. At nine to ten months, that’s when the shouting/screaming phase starts. Lets assume that as you say, he is fed and does not need changing. Form his point of view, he is trying to communicate something - we may not understand what - but that is what he is doing. He is literally finding his voice. Of course, at his age, he has no understanding of right/wrong, good/bad and so on, so if you scold him, you are teaching him that trying to communicate is not desirable. He’ll maybe stop shout anger, aggression or withdrawal. What to do? Don’t ignore him, but acknowledge to him that you understand he is trying to tell you something. Don’t "reward" him in any other way as an attempt to bribe him to stop. That way lies chaos! Try to relax about it, try to arrange your eating out to when there are fewer people around, and above all, acknowledge that this IS a phase and will pass fairly quickly, how quickly depending on the individual. The less you make of it, the quicker it will pass. If you can identify any particular instance what he actually wants, try to teach him to associate that want or need with a sound or word, or indeed a hand sign. It will be fun for him and you, and cut down his need to yell!
it seems that he just wants our attention. as soon as we pick him up and start to play with him. he starts laughing and happy as ever. but we don't have time to play with him all the time. he is now not just yelling during meals. he is also yelling in his play pen. as soon as we let him out so he is able to crawl around and discover things, he is ok as well because we have to follow him around (we have hard wood floors). but as soon as we walk away from him, he is upset and yells again.
I think you have to accept that nothing you do is going to stop him. All you can do is as I have suggested, and wait it out until the phase passes. When you walk away, and he yells he is still trying to tell you something, and yes, it should be acknowledged with a hug, a smile and so on –but no more. As you know though, if you then start to give in to him and pay him too much attention, he will quickly learn that yelling gets him what he wants! Try to ride it out - there is no easy solution at all, and every child ( and parent) goes through this.