2011 honda crz

i changed the oil in my transmission a few days ago, including replacing the filter. put in honda CVTF. also changed the battery, battery hold down, adjusted the tune a bit, and installed an intake duct. Everything done correctly as far as I can work out. Now, when the car’s cold, in drive, and moving forward slowly, it makes this rattling sound somewhere from the engine area, almost like a card in a bicycle wheel. if it’s warm it’s fine, if it’s cold and i’m over like 4mph it’s fine. Checked everything for loose parts, brackets, covers, shields, etc, all good. correct fluid levels everywhere. noooo idea what’s causing it other than possible internal failure of the CVT. any ideas?