Makes a rattling noise in park only,not in R,N,D,2,1. checked flex plate and bolts,all tight and no cracks. drives fine,shifts fine and no sign of metal shavings and no burnt fluid. 727 trans,10" converter. Cope manual/auto valve body,Lokar cable kick down.
Will be droping pan this weekend,just checking in on what possible things to look for.

Look at the starter bendix gear. It's possible that's what's rubbing against the flywheel, making it sound like converter noise.
It happened to me years ago on a rebuilt starter. Installed it, then hearing a scraping noise. The starter that was replaced made no noise.
Pulled off the rebuilt starter, looked at the bendix gear, saw some scraping. I put the rebuilt starter next to the bad starter. I noticed the bendix gear on the rebuilt unit was a little more forward than the gear on the original starter .The rebuilders shimmed the bendix gear too much.. Swaped out the starter with another one making sure the bendix gear was positioned correctly. After that no noise.
Hope this helps.

Check your crankshaft end play.

How do you check crank end play while all together? The engine and trans has been fine for 7 years. I dont see witness marks anywhere

Ok looked up how to check for crank walk,I can do that easy. I hope it's not that as that would be devastating.
the rattle is only in park though.could it be the converter is lighter in park due to less fluid being pumped in park so easier for the crank to walk back and forth?

There is no fluid pressure in the converter in Park, so a crank with excessive end play could wander back; pressure in the converter in other gears tends to drive the crank forward.

Just spitballin'.

Thanks John you guessed it! Engine only has a few thousand on it but the crank is walking just like you said.

Good news - you figured it out

Bad news - that kind of sucks

Good news Stroker Big Block

So did the bearing eat the crank or the crank eat the bearing?