What is (one) driving at?
What is one suggesting, alluding to, or insinuating? Often used when angered or irritated by what was said. What exactly are you driving at? I have never taken a bribe in my entire life, if that's what you mean! What is she driving at, bringing up my taxes like that?
What are you driving at?
Fig. What are you implying?; What do you mean? What are you driving at? What are you trying to say? Why are you asking me all these questions? What are you driving at?