It sounds like either premature atrial contractions (PACs) or premature ventricle contractions (PVCs) which I assume you have read the other threads about. If you are otherwise healthy and there is no underlying disorder causing them, they are almost always completely harmless. Get it evaluated by a doctor to rule out underlying disorders, just to be sure, but in the meantime try not to let it worry you too much. It can be scary but, once every few days, is probably a symptom of nothing more serious than a perfectly normal and healthy heart
. Most of the population has them occasionally; some people notice them and some people don't.