Dirty Ears in Hot, Humid Weather?

I've noticed both my cats ears have been incredibly dirty despite almost daily cleanings. They both just had their yearly check-ups. They had their ears cleaned there as well, just wiped out the outer areas basically. I was told there isn't any mites or infections in either of their ears. Even the vet noted they were seeing a high rate of dirty, waxy cat ears lately. I was wondering if it was weather related..hot, sticky, humid weather? Has anyone else noticed this problem? Just curious. 

Are the cats indoor or outdoor?  All 4 of mine are exclusively indoor cats and I've never had an excessive dirt or wax problem with their ears.  I know that outdoors with all the humidity around here their little ears would be catching all kinds of stuff in them and I'd probably have issues.
 

They are both indoor..usually, their ears are just fine..they don't appear to be in pain, there isn't any odor, etc. Just find it curious and a bit frustrating not to be able to keep them clean. I don't want to hurt them or cause injury so I guess I'll just have to learn to live with it.