Strange noise

[Braunchitis]

I have an 86 M1009. Today I started noticing a kind of grinding noise coming from what seems to be the flywheel area (maybe?). It only seems to do it when I'm in park, and when I'm giving it a little bit of throttle. It stops at higher speeds and when I'm coasting. Fluids are full. Does anyone have any ideas?

 

[truck0590]

When that happened to me, it got louder and louder. When I checked it, it turned out the flexplate bolts had come loose and 3 were sheered off. Could be the same or a cracked flexplate, which is what I was expecting.

Truck