Ford Repair: fly wheel or torque converter, torque converter, flex plate

Question
F250 Ford truck 4 X 4  heavy duty off road suspension..1999..diesel.
making noise that sounds like marbles swirling in a 55 gal drum....when at idle...no noise when excellerating....some say might be fly wheel...should change and put 1-piece.
another says have to take off torque converter to replace flywheel...so is probably not fly wheel...probably is torque converter.
Any suggestions?

Answer
Hello and thanks for the question...I'll try to help.
let's get the terminology straight... A standard transmission has a flywheel....an automatic transmission has a flex plate. Either way, the transmission needs to come out to replace either the flex plate or the torque converter. You can also have the torque converter checked while it's out on the bench.
Erik