I've got a 2017 Edge Sport, purchased used 6 months ago.. Nearly same issue as tuffsubject.. Subwoofer buzz is there when engine is running and audio is off. When i turn headlight switch to different modes, the pitch of the buzz changes frequency based on the mode setting, but does not stop buzzing with any mode including off position. No other functions seem to affect the buzz. Dealer could not find root cause, no components have been replaced. Gut feel is that it is a wiring issue. I reached out privately and learned that tuffsubject's issue was finally diagnosed and fixed - a bent pin in a wiring harness connector in the console causing a short. I'm guessing my issue is similar.
