What is your history with the machine? Is it a sharp knock or more "deep" and internal? Some have mentioned exhaust/manifold leak. I would go with that if it is a sharp tick.
This won't be a popular answer, but my first thought internally was rod bearing. I had an IH engine that did that and it was eating rod bearings. It still had high oil pressure. Those letter series engine make about double the oil pressure an N is set at, so the oil pressure might be a better indicator on the N.
If it does it all the time that means something different than if it is only after an hour of running when the oil is thinned. In cold weather rod knock is usually a little better just because the oil doesn't get as thin when it is 10 degrees outside.
Same-Day Shipping! Most of our stocked parts ship the same day you order (M-F). Expedited shipping available, just call! Most prices for parts and manuals are below our competitors. Compare our super low shipping rates! We have the parts you need to repair your tractor. We are a Company you can trust and have generous return policies! Shop Online Today or call our friendly sales staff toll free (800) 853-2651. [ More Info ]
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.