Easy answer: Install a strut tower brace under the hood.
Long explanation: I bought a used a 2008 Mustang v6 convertible. When I back out of the driveway the creaking sound drove me nuts. The sound was exactly the same as 60's muscles cars sounded in the 1980's. It was always the frame. It needed the grease fittings to be greased, but these cars don't have grease fittings. So many people listed a ton of solves including wheel bearings and other stuff. BUT the sound of a frame noise is unmistakable, its like old bones creaking. For me it was in the morning backing out f the driveway..... creeeeeaaaaak! My thought was to lubricate everything, but since I bought the car a few moths ago I never liked the way it handled corners. Way too much sway or maybe what you feel is "tilting" as you turn. So the cheap solution was to add a strut tower brace to help that. WOW I put it on in 15 minutes and not only was my ride 100% better, but the creaking is completely GONE! WOW! It was the frame all this time and adding this stiffened the frame and resolved everything.