First off, I want to apologize for not having a video, I know these knock threads are incomplete without one. But the knock is intermittent, and often difficult to distinguish from the engine noise. I also don't want to try to use the camera while driving. But I know my truck, and I know it's not normal.

It started immediately after my accident last fall (thread: https://www.yotatech.com/forums/f116...-worse-222721/ ). I've put over 800 miles on the truck since then, so I highly doubt it's a blown engine. Here are the requirements needed for the knock to start, if any of these aren't satisfied, it goes away.
-Engine must be warm
-truck must be stationary with my foot on the brake
-tranny must be in "drive"
I change any of these and it INSTANTLY goes away.
My only idea was that it was the fan hitting the shroud, but I just replaced the fan clutch and triple-checked the fan clearance in the shroud. It's at least an inch all the way around. I'm out of ideas.

 

Can you duplicate the problem, say on a steep hill, or with a heavy load on the engine? I have an exhaust leak, and with the right conditions, I can hear the valves rapping.
Either way, might want to check for an exhaust leak.

 

Is the inch shroud clearance with the trans in drive or park ? A motor mount may be bad.

 

cyberman- I can duplicate the problem any time I want when all three requirements are met. I can give the exhaust a check, but I don't think that's the issue. The knock is deeper than valves "rapping".

swampfox- The inch clearance is with the trans in park and the truck cold. It would have to move a LOT to hit shroud, I don't think I'd miss that kind of vibration, correct? I'll have to give both motor mounts a good massage tomorrow and see if they feel cracked.