One day this old lady walks into the doctors office and is shown into a room. When the doctor comes in and asks what the problem is she answers, "I have awful gas, but it doesn't bother me. You see, it's completely silent, and doesn't smell at all." 

So the doctor, after examining her thoroughly gives her some pills and tells her to take one everyday and come back in a week. So the old lady comes back, and when the doctor asks if her problem is any better she replies, "Well I don't know what you gave me but now my gas smells terribly!" 

The doctor replies "Well now that we've got your sinuses cleared up let's work on your hearing!"'