In the shoulder you should look at internal and external rotation in a neutral and abducted to 90° position to see if one of those causes something to click or pop. If so then you have to figure out where it is and if it’s painful etc. could just be a muscle or tendon slipping over a bone. Also look at AC joint mobilization, and how well your SC joint moves.
Back is more complicated because it could be scapular related, spine related, clavicle related etc.
Also look at your posture for rounded shoulders etc