My granny had this. I can remember she used to have a thing about eating around other people because she was always worried she would choke, and had a constant feeling of something being stuck in her throat. They never could find anything wrong with her throat (she lived to a ripe old age and definitely didn't die of anything throat-related).

Try to be reassured by your physical exams - the camera would have picked up any obstructions in your thoat. The fact that it does go away sometimes suggests that there isn't anything growing in your throat because if there were it would not go away. Has you doctor suggested a diagnosis?