Just an idea, is it your precats ticking, low knock, my 2000 f150 5.4 has this, 118k, goes away warm and in gear, I narrowed it down with a steth, and a hose, my drivers is worst than the pass. Ford had a tsb on this and their fix was sound deadening wrap. I just haven't mustered up the 700 for new assemblies, aftermarket by walker.