Mowing D110 19.5 HP suddenly very loud exhaust/compression noise

[Phil P]

While cutting the grass this morning my John Deere mower suddenly changed its sound from the usual to very loud exhaust popping noises. It was not backfire. It sounded as though there were a hole in the exhaust. I have taken it apart and found no holes and no obvious leaks in the exhaust. It seems to run about normal just incredibly loud.
I need ideas on what to try.

 

[beenthere]

Maybe rusted out muffler innards?? How many seasons on this engine?

Or, if you've lost power too, then maybe a valve problem.

 

[Looking4new]

You probably just burned the guts out of the muffler. That is my edumacated (I know I cant spell) guess.

 

[Wagtail]

Does it sound like the choke has been engaged?

 

[Phil P]

Five seasons. Stored in garage. Never wet except to wash it off. I took off the muffler and can hear no loose stuff within.

 

[Phil P]

No loss of power.

 

[larboc]

Assuming briggs and stratton? Those are fairly solid engines. Possible the head gasket blew? The early ones liked to bend pushrods and have the decomp cam stick but I don't see how that could cause your issue.
You need to see if you can find where the noise is coming from. Video with audio?