Under heavy acceleration, typically around 4500rpm, I am getting fast and loud ticking sound.

I have done some research and found that worn timing tensioners and crack timing chain guides can cause this sound.

I am not sure if it is timing chain slap!

There is a similar sound I hear after the engine has settled soon after starting, when the idle has dropped to normal speed.

There is no clunking sounds to be heard. Just that fast ticking/rattle.

Has anyone else experienced this?

Also, I have been running BOSCH Iridium plugs. Could these be NO NO? Perhaps overheating, not operating, or anything that could potentially cause spark know.

and on that note, can spark knock be heard at high RPM's. I know typically it is at low engine speeds. Any ideas?

 

Issues with timing chain tensioners and so on were 'put to bed' before the X350 Series came out in 2003. However, that's not to say you might have some wear in there. What miles on the car ?

 

96700 miles. I bought it with 76000.

 

Hmmm, should be OK with those miles, but the VVT units can wear a bit, I believe and could cause a slight noise.

Of course you could always check the tappet clearances to see if they are OK. This would also allow you to inspect the top timing chains.

 

My VVTs on my 2003 XK8 are really loud, at over 150,000 miles. Same engine, so could very well be the same symptom of age. Usually after some oil circulation, it diminishes a bit.