Sometimes cats will get a residual build up of wax and gunk. My cat Maxwell had earmites when he was a wee baby and we treated them and got him all fixed up, but to this day, 3 years later, the poor cat still gets the extra ear wax and dirt build up for no reason. I have to regularly 'scoop' it out.. it takes about 5 q-tips to each ear to scoop all the muck out. It's pretty gross too. We've retested him so many times and no mites! All my other cats have normal kitty ears. Poor Maxwell though