Hey Scotty, I have a 2004 v6 automatic mustang with 125k miles. Around 105k miles my car started randomly making a rattle from what sounds like the engine when I accelerated and it’s been slowly getting worse. Now it is a loud rattle that only occurs in third gear or higher and only in certain parts of the throttle. The rattle sounds like a metal on metal rattle and it only happens between 2000-3500 rpms and it does not happen is first or second gear or at idle, so I cannot listen while revving it. Also, it is the loudest when I am going up hill and automatically stops when I let off the throttle or accelerate harder. My car has a p1336 code which is labeled as a misfire monitor hardware code and a reported fix is the camshaft position sensor and sycroniser assembly. I replaced both but it did not fix the nose. I also turned the crank and it seemed like the timing chain was not stretched but I am not absolutely certain that it’s not bad. This link is to a video of the sound happening, you may have to turn up your volume to listen but it is much louder in person. https://youtu.be/b5B-k5Ot1oY Anyone who has an idea of what it could be please let me know. Thanks.
at that mileage is to be something as simple as a heat shield out of place or a plastic cowl that is flapping around while you're driving check that first worst could be it is a piece of the catalytic converter that is rattling inside