Help! Adolescent Chow mix demand barking Any advice on how to curb demand barking in a 15 month old adolescent chow mix?

It isn’t due to lack of exercise or needs like going outside or needing water. We will get home from an hour long walk and he’ll demand bark. We will be sitting on the couch after a walk or even after playing outside, or maybe he just randomly looks at us and won’t stop barking. When this happens, we ignore him (don’t make eye contact and then engage with him once he’s done). However, he may bark for 5 minutes straight and sometimes it takes going into a different room and shutting the door (is this the wrong move)? 

Recently he’s started to nip our clothing and paw at us in addition to the demand barking and it’s not acceptable — and I’m worried this behavior might get worse in time? Overall, he’s a quiet dog but when he gets in this mode, it’s so loud, startling and I also worry about this behavior disturbing neighbors. Any help would be greatly appreciated!