6m old Kitten has black stuff in ear

Our Kitten is 6 months old and one of his ears has some sort of black goo in it.  I cleaned it out last night, but it seems tender and the goo is back this morning.  I guess this means another vet visit.  We've only had him 2 months, but he has been to the vet 3 times already.  I'd be surprised if this is ear mites as he is an inside cat and has been checked by the vet several times already. 

Anyone know what else this might be?

Thanks!

It sounds like ear mites to me. A quick visit to the vet is in order. 

It could be earmites, although, if he's an indoor cat, it would have to be some long-term infestation that is only now manifesting itself.

More likely is a yeast infection, which isn't uncommon.

If it's earmites, the easy way to treat it is with Revolution.

Just fit back from vet. $57 later... Cat has a bad ear infection. Black stuff is a mixture of puss and blood from scratching. Got Tresaderm meds - drops for ear. Should clear up quickly. Been monthly visits with this cat since we got it. Sickly Rescue cat.