I have one--Harley my b&w boy is an ear sucker. It most likely relates to the fact that he was taken away from his mother to soon. Harley does it when he's trying to go to sleep, he sucks until spit is rolling off our ears. We let him do it for the most part because we know he finds comfort in it--although at 4 AM it can be a bit disturbing.
My cat Easy does it, too. I also let her do it because I know its comforting to her. Although, she does it less and less the older she gets. How long have you had your cat? As Leslie said, some kittens who are taken from their Mom too soon do this, not necessarily on the ear.
My siamese cello does this. I have no history on him, not sure if he was taken away from his mom too early or not, but he is atelast 8 or 9 now and he still ear sucks with avengance, and I let him, because he purrs so loudly when he does! He also kneads with his paws while he does this!
Not sure what it is or why!! It's gross but I let him.......
Ive had him for about 9 months he was a skinny scruffy stray and already a grown up kitty by the time I got him, I know what you mean by the 4am wake up call and I refuse to declaw my cats so I always have scratches on my neck from him kneading, he usually does it at night when he goes to sleep (and hogs my pillow!). I don't know any of his history but are happy to find that other cats do the ear sucking too! Here is a picture of him:
My Pipsi did this right from when I first got her (she was 8 weeks which is young but fully weaned) she gradually stopped doing it, and after about a year stopped completely. What made me laugh was towards the end she'd come up to me, sniff my ear, give it a tentative lick then pull a face (I'm sure!!!) and walk off, I obviously wasn't to her taste any more!