Bought a 3910 going on a couple of years ago. Had the short oval muffler under the axle. Roar was deafening. Thought the muffler was bad. Bought another short oval muffler....noise was deafening. Figured all that pipe was resonating. Reconfigured to vertical including a new exhaust manifold due to positioning, and new hood with the exhaust hold forward of where it is on my 3000 and bought the longest oval muffler I could find and it just happens to fits the OEM spec for that tractor in the cab version......noise was still deafening.
Happened to be standing next to it a couple of days ago and picked up on the the fact that the long sides were vibrating....so here i have a supposedly sound deadening device that is playing it's own tune. Bah Humbug.
Went over to my 3000 and pulled the FO-17 round off it and put it on the 3910, put my ear up to it and no rattling.....aah tolerance at last. Today the new FO -17 arrived, installed it and no more drive you nuts noise....not whisper quiet mind you but tolerable.
So, the next time somebody says well, some of a certain vintage tractor are just noisy and some just aren't all that bad, might have a look at the muffler type. I posted this because my engine is just rolling 1000 hours and that's just a bit early for a farm tractor, especially of that vintage to just fall apart, even with sloppy maintenance....which this one didn't have.