My boyfriend's dog has been scratching one ears alot since I moved in with him my dog and cat has a problem with only one ear. I thought mites at first but now I am not so sure. When we wipe his dogs ear out brown stuff is what we get. if it is let go for some time a smell occures.
This sounds like an ear infection which could be mites, bacteria and/ or yeast. Your pet should be seen by a vet for this. Ear infections can be very painful. Good luck, vetcare