The important thing is your GP said there is nothing there, and I presume you did a swallow for her. Perhaps you are over-analyzing your body.
Hello~I doubt if it is anything serious, it possibly has always done that but you are just now noticing it. It is more than likely muscular in nature. Try not to obsess about it, I am sure if it were something serious, your doctor would have run some tests to rule out thyroid disorders. Believe me, anxiety and stress over health can cause all kinds of weird thoughts, LOL, I should know, I am an expert at it.