Aural Hematoma's are caused by excessive shaking of the head, excessive scratching, or rubbing the ear due to itching, or pain in the ear from an ear infection or ear mites or both.
These actions can break the delicate capillaries in the ear pinna causing a pocket of blood to fill up and since there is no outlet the blood has to be removed in a procedure either with a needle or with a surgical procedure. So I think that your cat is bothered by the ear problem. The best option is of course to have your cat seen by your vet since not doing anything will cause the ear to fibrose down into a cauliflower ear, like a prize fighter.
sorry, I forgot to mention that my cat is about 9 years old and vey active. I have read everything I can about his ear and come to conclusion that it is a hemetoma on his ear. I do have 1 other cat in my house and 2 dogs. They all play pretty ruff, would that be how he got this on his ear?