see if the existing oil is not all black or has particles in it! if so, change it, clean the filter, clean the oil pan and put a new gasket on the pan if & when it is opened -- also, pan contains a magnet sort of ring that keeps the metallic particles from circulating with oil,see if that magnetic ring is okay.
there is a sound in my gear -- feels like coming from the torque converter, if i'm correct
but it comes only at a particular RPM not on higher or lower or any specific gear.