This may be difficult to diagnose but first the obvious checks, oil recently changed? If not diluted oil may be an issue. Can you tell if the noise is from engine, transmission, transfer case area? Does the noise change when in gear? Idle? gentle rev in park - does the noise change? These will help pinpoint if the noise is from engine or drive train. It could be an accessory drive issue. The way to isolate that is pull the belt and start the car, do not leave it run long, but you can isolate all accessory drive components. Last idea, post a video so we can hear it.

 

good advice, keith64.
I'd also suggest telling us which PART of the motor/trans/t-case. ie: top or bottom? front or back? Sometimes a person can really isolate the vicinity of the noise with a long screwdriver. Use it like a stethescope... no, I'm not kidding. Place the tip agaisnt various parts of the motor, and your ear on the other end. You might be surprised.

and is it low-pitch or high?

 

and does it go away when you rev the motor?
Does it get louder if you take off the oil-fill cap?
When was the last oil change (miles and months) and what oil was put in it?
(Have you checked the oil level?)

 

Very difficult to pin down. Mine began to sing the knock knock joke and I shut her down until I perform surgery. The knock I heard was consistant with RPM and it sounded like it was serious but did not suffer engine stumble nor performance. It sounded to me like a spun bearing. This is a connecting rod that has worn down its insulator, for lack of a better word, between it and the crank shaft lobe. It sounds like a jack hammer. With my engine running I poured 1/2 quart of oil down the spout on top of the chain. After a moment or two the knock stopped. Then it returned after 10 or 15 min. At this point I changed my mind about the problem being a bearing and thought mabe it was "chain slap" instaed. However I have never heard chain slap/rattle like this before. I have pulled off the front cover and the rear chain can be pressed in by 3/4 to 1 inch. The front does not move even with lots of pressure. I am still in the process of removing the powertrain so I don't know for sure until a I look inside the oil pan, look at the crank and rods and carefully inspect the valves. But right now I am convinced that the Chain Tensioner is the issue. I googled the jaguar chain tensioner and came up with alot of complaints about failure but these articles were not for the x-type v6 model (V8 XK/XJ). I will find out for sure pretty soon.

 

Are you really sure it's a knock and not just valve noise? Or the tick of injectors? Some of these noises are rather normal. Does the car stumble or hiccup? Any smoke out the tailpipes?

 

I'm sure you've seen this, but if you haven't, read this thread carefully. Does this sounds like your problem as well?

https://www.jaguarforums.com/forum/s...ad.php?t=10670

 

If it is a knock I would assume that you spun a bearing. I had the same issue with my 88Monte SS. Cold the motor was fine but when it got warm it had a bad knock from a spun bearing.

You should look into it more and do what the other guys said and check the oil and such to make sure you cover all the bases.

 

Pete,
At first I thought rod bearing but after pouring oil onto chain and it stopped I decided chain noise. This was the same sound I have heard from "rod bearing failure". I too have spun a bearing, it was a 86 Toy pick-up. No smoke. Removing valve cover futher lead me to beleive chain tensioner failure since I could press down the rear chain and not the front chain. Once inside the front cover I could press the rear chain almost an inch, front would not budge. I swore I spun a bearing but the evidence is not pointing to that yet. Not a tapping sound of a valve, not the "rattle" of a chain, not the "psst" of injectors but is had that deep jack hammer sound. I will know more this weekend. I do plan to check out all the rods and valves this weekend even if I find nothing in the pan.

 

I'm also having a slight knocking sound. It sounds like it's coming from the oil PAN. It's in between the PAN and the transmission. I am having a transmission fault code. I know that my gear oil is a little low and I'm throwing a high Volt noxenter code knock sensor it doesn't make sense all of a sudden if I have a spun bearing. Would like input