I was mowing today, normal 7 acres, nothing out of the ordinary. Got about 2 hours into the job, shut it off to eat lunch, started back at it about 30 minutes later and the engine is knocking high/mid/low idle rpms. When I throttle back from full rpms, it has a horrible whine along with the knock. Motor has about 1800 hrs on it. Oil is full, even added a little hoping it would cure the issue. Rod knocking?