GT 2186 Sudden Engine Noise

[SteveInBerks]

Hi Gang, and thanks for having me here.

I bought this GT 2186 at a local auction a year ago. The machine was relatively well cared for, and the auction house put in a new battery and new fluids. It has a Kohler Command 20 under the hood.

I've run it for a year with no major issues to mention here (I'll mention them in separate posts), it hasn't burned a drop of oil or tranny fluid, starts easily and runs like a champ. I mow and maintain (hauling sh*t around with a wagon) about 2 acres of hilly grass on our land, and currently have 770 hours on the machine... don't remember what it was when I bought it, just that it was over 700.

A few days ago I was doing a "third round" on our land, meaning I was lazy and mowed the land in zones. This last round took about an hour or less, and I've spent 2-3 hours running the machine with no mechanical issues.

Anyway, about 35 minutes into this last mow, the engine began to sound much louder than usual, and then added a loud knocking sound. I stopped the machine, checked the belts, oil and undercarriage, no issues, started it back up, finished the last bit of mowing and took it up to the barn.

I shut it down, walked around a bit and then started it up again, and it sounded "almost" normal again. Checked everything again, no leaks, no holes.... put it to bed and let it alone for a day.

I took videos in between the parking, and starting again, links below.

Yesterday I started it up again, seemed just like normal, no loudness, no knocking. Shut it down, checked oil and tranny fluid, both full and really clean. Opened up the air cleaner, it was a little dusty, mainly the foam wrap on the air filter, but mainly clean. The area around the carb had a very light oily film on the metal frame (photos at second link), but the air filter itself was not "oily'. I did not check the fuel filter or pull the spark plugs, as the machine still starts normally and without issues.

Any thoughts? It wasn't a very hot day (mowed for hours in the 90's with no issues a week before), and I wasn't pushing it very hard, so I'm concerned. I don't just want to say "Well, it went away, no prob" and keep going as usual if there's a serious issue I need to deal with before it becomes something I can't afford.

First link - Video 1 and 2 are the bad noise, third video is after I left it alone for 20 minutes.

https://photos.app.goo.gl/pLWF2KKae2pkAroh8

Second link - Two days later, video of it running nice and parts exam photos.

https://photos.app.goo.gl/bBwh769sQRtBfH4F9

Thanks in advance for any wisdom!