I have a 2003 XJ8 with around 120,000 miles. It makes a clacking sound on cold start that has a frequency of around 400 bpm and rises with engine rpm. This sound quiets at rpms upwards of 2,500 rpm and goes away after the engine is fully warmed (I assume this means that higher oil pressure alleviates whatever is causing the noise). Even though valve train issues are rare on this vehicle, I believe that the sound is from excessive valve lash. The car was not driven leisurely in it's previous life: the previous owner said he like to keep it in sport all the time and there's a burn on the oil dipstick (yeah, honestly no clue mate). This sound has existed as long as I've known the car (since 100,000 miles) and I thought nothing of it. However, recently I listened to another jaguar's engine on cold start and it made no such sound.

When I get a chance, I'm going to peek around with a mechanic's stethoscope and also try taking the serpentine belt off in order to make sure it's the valve train. I saw in a previous thread that a loose spark plug made a similar sound, but I already changed and torqued spark plugs so it's not that.

In the meanwhile, can y'all think of anything else that could make such a sound? Additionally, do you guys have the links for buying valve shims? I'll need the valve clearance specs too. If y'all could provide links for cheap timing tools as well (I plan on taking off the camshafts for such an endeavor), that would be helpful!

 

I had a similar noise that ended up being injectors ticking. I had two that were the loudest, and after replacing them it's much quieter. Poke around with the stethoscope like you said. That's how I figured out what my noise was. I thought it was the valves at first.

 

One of my XJ8 (2000MY X308 wife daily driver) sedans has what I think is an audible 'piston-slap' when cold.

I don't really care since it has done it for years and gets quiet when the engine warms. (always sounds the same, louder when she leaves, quiet when she returns)

Pick-your-battles when you determine what you want to tackle.
I have spare Jaguar sedans and XK convertibles (and engines) so I just 'go-with-the-flow'.

 

Not sure obviously, how exactly your "clacking sound" sounds.
I had a "clacking sound" since I bought my X308, but I knew all along what it is: broken timing chain guides causing the chains to be slack. Noise always there when starting and disappearing after a short while. I did however not count the "beats per minute"... - btw.: the unit for "frequency" is Hz (Herz), not bpm...

I am currently in the process of fixing my "clacking sound"...

 

I have the same issue with one injector. First I thought it were the valves, but the stethoscope gave me the hint to the injector.

 

It is rather odd they can make such a racket....but it is true.

 

My 01 XJR makes a bit of what I would call piston slap when stone cold from sitting overnight. Does it for about a minute or two and then it warms slightly and thats all I hear from it. Was thinking I might go to 5w-20 when I do my next oil change and may run some seafoam through the crankcase just before I change the oil to clear up any invisible deposits. Other than that I've got no clue...hadn't considered injectors so maybe some fuel system cleaner will help, but I'm not too concerned about it, my GMC pickup has made this noise when cold for as long as I've had it and may old 2000 Chevy Silverado did it for a good 100k miles without issue.

 

Any one that is experiencing this problem may want to check their ignition coils firsts. I recently had a tapping sound that I thought might be excessive valve lash. I even removed the valve cover and checked the valve lash clearances with some feeler gauges. Clearances were good. Then I wondered about the possibility of a defective coil. I removed the ignition coil cover and using a long screwdriver as an improvised stethoscope, I touched it to the top of the coils with the engine running. I could hear and feel some noise from one of the coils. I moved the coil and the noise moved with it, indicating an internal defect in the coil. I have a new coil on the way. Sure a lot cheaper than a rebuild!