doesn't sound good to me, but that being said I would take off the belts and start it up and verify that it is not something else, i.e. power steering, water pump, ac compressor, alternator. If the sound is still there then try and look at the fly wheel with a flashlight and mirror thru the inspection plate look for any cracks, get underneath it and see if it might be transmission related or not or if it could be a loose heat shroud, catalytic converter, etc. if nothing pans out then pull the valve cover as mentioned already.
you can also do a oil sample and see if there is anything dramatic going on.
I had a "similar" sound once and it turned out to be a loose bolt in the torque converter but I had a general idea it was transmission related at the time because I had recently had it worked on and the sound was new.
I am just being optimistic, good luck