Lets try to narrow things down some.
Is it clanky with the engine running but the mower not moving?
Does it only clank when cutting grass or leaves?

Hi roadbike,

Thank you kindly for your reply.

The blade is always running when the mower is started.

And it is clanky whether cutting or not cutting.

Oh, and it is self propelled.

And it is clanky whether it is being self propelled or not.

Thanks in advance for any help.

Well, something is rattling or hitting something. Items that come to mind are a bent blade or bent crankshaft that causes the blade to bang against the mower body. It could be a muffler as well. I would strongly suggest that you ave the mower looked at by a lawn mower repair shop. You may very well have a problem that could cause damage.

Thank you roadbike.

I'll post the answer to my problem once I have it resolved.

Maybe it will help someone else.

I really appreciate your efforts. Peace and good health.

Maybe the blade has come loose. That would certainly make a clanking/clunky sound.
Turn the mower up on its side, with the carburetor on the high side, remove the spark plug wire, hold the little thin handle back, or tape it back, and wiggle the blade.
Then try rattling any grass deflectors that surround the blade area. They do work loose. See if they might be contacting the blade as it turns in its arc.
When i go around my yards, mowing and blowing leaves, there is always a considerable build-up of grass, dirt, chopped leaves, and other crud, and it makes a nasty sound eventually resulting in a good clean out of the mowing deck.

Check the engine mount bolts too, but this would have nothing to do with the rough running. Another thing to check is the flywheel. You'll have to remove the plastic tank shroud and the steel air shroud to see the flywheel. Try to 'rock' it on the shaft - if any movement, take it off and see if the key in the shaft is bent or sheared off. If so, replace it. If the flywheel is loose, it could knock, and ignition timing will be affected which would make it run rough.