Does it only happen when the vehicle is cold?

 

My vote is for oil system related. To me, it seems like the knock occures until the oil system builds pressure. Either something at the top end or the pump itself.

 

The knock usually only happens when the engine is cold. I think that it is the engine stuttering a little on a cold start and the extra vibrations are causing something to knock.

I wonder though if it is the top end of the engine. I have noticed while driving that sometimes while accelerating I can hear either the valves or the fuel injectors, although maybe that is normal for these engines.

 

Mine just started doing this a week ago. First time I heard it I had to go and look under the hood because I thought something made a nest in the warm engine over night and got stuck in the belt. It just did it again this morning. To me it sounds like it's coming from the front of the engine. A kind quick grind then low knocking and engine shaking for about 5-10 seconds. Maybe one of the pulley's sticking? Any ideas? I have no engine mods.

 

same problem here, dealer couldnt find it...

But mine is a manual trans as opposed to most of the autos posting... so definately engine related

 

I have the same problem. I am not sure what it is. It sounds like the exhaust. It only happens when the JK has been sitting for a few hours. I think somebody posted something about the exhaust manifold bolts coming loose. Has anybody seen this?

 

I got my 2door manual X in early WV winter, seems to be temp related like the rattling shift knob. Thinking trans. bushings.

 

if the sounds like a "thick-thick-thick" metal type sound and it slowly goes away your lifters are dry and starving for oil i've had that problem also i recently switched to syenthitic oil and havent heard it not sure if you kno about syenthitic oils or not bet if you switch DONT switch back also you should let your engine sit for a few days to let the oil drain down then change it drive for about 1500-mi or so and change it again to make sure you get all the hd oil out then your good for 8000-10000 mi between changes depending on driving conditions i change it 3 times a yr and to the question of "DONT switch back" thats what i have been told

 

Had the same problem in my 08 x unlimited manual trans. I switched to synthetic oil and problem solved...haven't heard it yet

 

mine has just started doing this same thing about two weeks ago its not cold here 80s and 90s wife thinks its the topbut its not that. I wunder if i put a quart of Lucas oil in would it go away if it is engine related