Yeah it does sound kinda nasty.

Def not a broken flexplate, they sound insanely bad, and typically the sound goes away once you rev it a little.

I'd get out a stethoscope, or a screwdriver, socket extension etc. and start poking it around and listening. It could be the alternator, the one on my GT was always noisy as hell until it caught on fire.

Just press it up against different points, and try to find out which point is the loudest. That should help narrow it down