Your converter is toast, fubar, coming apart. Don't drive it any further or you could wipe the engine crank thrust bearing or damage the tranny if it ain't allready to late. Have the converter pulled and inspected, I suspect broken vanes on either the pump or turbine disk.
The torque converter is made up of 3 seperate parts (4 if it's a lockup). The outer drum is bolted to the flexplate is called the pump and has internal vanes that pump the oil through the internal turbine disc, turning the disc as it does, which is connected to the input shaft of the tranny. The turbine disc also has vanes all the way around it which capture the flow of the oil from the pump (drum) and converts that to rotation to rotate the tranny. I almost forgot the stator, it directs the oil between the pump and turbine among other things. I suspect that 1 or more vanes on the drum or turbine have broke off which will sound like a chain saw as it rubs internally and also not allow the turbine disc to stop turning as it has to do when idling in gear. I suspect that when you put the tranny in neutral everything seems fine.