Very loud rattling sound. Transmission
 

Hello everyone i noticed a very loud rattling noise coming from under the truck. all original 2001 ranger xlt 3.0 Automatic trans 2WD with 334k miles. It'll make the rattling noise when i apply brakes and give it throttle or when accelerating from a stop. Its super loud. Its definitely the trans because when i put it in neutral and give it throttle it wont make the sound ,engine revs and runs great . It doesn't do it when im at a coast either. All fluids changed at correct mileage. There's no play in the U joints or drive shaft , nothing loose either from what i can tell. There is also no slippage in the trans. Anyone have an idea what it could be ? Maybe the splines ? Thank you for your input and time !