Was sitting down with headphones then my ear started to hear a heartbeat sound and it went to super fast and then it stopped and kept on when i yawned?

Ear: Great question. Couple of things could cause that. Sometimes the headphones alter how your eustachian tube equalizes air pressure and you are hearing the tube opening and closing; sometimes with the headphones on, you are hearing your heartbeat and there is a little tendon attached to one of your ear bones that contracts in response to loud sounds. See an ENT to check it out