Perhaps I am just living in denial, but I would like input from the board. I have a 2001 XJR with 67,000 miles. I have had the car since it had 22,000 miles and it has been well taken car of.
For about 6-8 months, upon start up the car sounds like a diesel engine. If you give it gas in park, or drive for about 2-3 minutes the sound goes away. I was at first fairly convinced that the tensionors were going. However, I have do doing more reading on the board, and have learned that this is less common in the XJR's since the engine does not use VVT, like the XJ8 engine.
I don't think the noise is getting worse, but I am still concerned about it, as I know the risks of continuing to drive on it if the tensionors are going. I have had no lights or warning messages related to this. Is there anything besides the tensionors that could be the cause of this issue? I am going to drive the car for about another month, and sell her, so I don't want to pass along this problem to a new owner..

 

You may have chain guide problems. This, too, is a known problem area.

KS

 

I have noticed the same issue with my 01 XJ8. I have had all the tenisioners & guides changed within the last 3000k miles and hate to hear the knock. It did do it before the tenisioner repair also. I read on another thread that it may be the oil that I am using but I have had synthetic in the car since it had 7k miles. I literally goes away within 30 seconds of driving.

 

Try a can of 'Restore' added to the oil. Can't hurt and might tell you something about the reason for the problems.

It just up's the viscosity of the oil.

 

Could this be the EGR valve just being open when the engine is cold? When it warms up, it closes and noise goes away?

2001..... hmmm... at some point the started using the "good" tensioners but I don't know when the cut off was.

I replaced my 99 XJ8 tensioners and when I got to them they were nearly destroyed.. So I dodged a bullet.

If you really suspect them, I would take a valve cover off and have a look. If they break, it will cost you dearly....