does it in neutral as well, everything leads to flywheel/flexplate or torque converter as it does it in every gear and neutral at an idle only...and the discoloration on the flexplate also leads me to believe a weight has came off somehow. the only other option that it may be is something riding free on the torque converter. I haven't had one off of a 02 and newer car but memory serves converter just slides over shaft and has 2 notches that fit around the shaft. I need to get a look at a parts list that shows the converter going onto the shaft to see if it is still like the older converters, to see if any pins are keys may have been able to have been sheered or broken. (and no to stethoscope, used a cut down broom handle)