Its very faint, but you can hear some scrapping to it. Check also your starter, it could be loose and it's up against the flywheel. My 80 coupe did that and it was sounding awful when starting up and when idling. I took a looks see and the starter was cracked and had chunks kissing which I found on the dust cover. I replaced it but soon after, I parked the Caddy and got me a new car, my caddy hasn't been driven since July of last year.
You can do what csbuckn mentioned as well. On my 80 brougham coupe I had, it had the exact sound and was told it could be something minor or major. Minor- flywheel, major- engine rod. The method used to check it was unbolting TC from flywheel, if sound ceased then that was the culprit. If it didn't, engine rod, crankshaft bearing..in my case it was the crankshaft.
Hopefully yours is something minor...best of luck and keep us updated on what you find.