So I finally got it today. it has a stumbling problem from time to time, I opened a thread o this but I will have it addressed next week.
Here is a video of the engine. I hear a slight rattle sound coming from a place that looks like timing chain to me. The engine is "new" the original engine was replaced with this one which has 60000mi and the transmission is rebuilt. The mechanic told me that the tensioner problem is addressed. Anyway what about this sound ? does it look weird ?
I never had a xjr before so I can't tell.
thanks a lot.

 

Do you have an engine stethoscope to help you dial in the area of the noise? There's a couple things that could be making that noise, one being the tensioners, the other the SC coupler. Another cheaper easier possibility could be an idler pulley bearing.

 

I suppose that if they are the tensioners it's a bad thing... right?
here is the area where the noise is coming from

 

That's probably tensioners, perhaps only the secondaries. You can remove the cam cover and view them. Look in my sig under the How To link and find a link by blackonyx which will be on replacing both primary and secondary tensioners, guides and chains. But the pics alone will help guide you to what you will view when removing the cam cover.

 

Can the car still be driven or needs immediate attention ?

 

Check the tensioners before driving or it could be fatal to the engine.

 

Had a very similar sound. Appeared to be coming from the same location, on inspection secondary's were fine, ended up being a stuck primary. The XJR's have less timing issues (no VVT), but age, mileage, and maintenance failures are still possible. Its a Now/ASAP repair/inspection.