Yet another N62 engine knocks like a diesel - E53 X5 4.8is

[danny_acs]

Hello everyone! I've searched the internet and various forums for weeks now, so I am not posting without doing my proper research. I haven't seen anything out there that is analogous to my issue, so excuse me if I have missed something. I've literally spent weeks searching and reading, but no result. Here is the issue along with a video clip, I do hope that someone else has experienced this or has an idea and might be able to help.

My X5's engine has developed an intermittent (i.e. not constant) knocking sound only when stationary in Drive (D). This is when the engine as under a small load in Drive, and the RPM's drop slightly below idle speed. The knocking sounds a bit like a diesel, goes louder as the RPM's drop a bit further (as the AC compressor kicks in or I turn the steering wheel), and completely disappears in Neurtal or when the car starts moving. Almost as if the timing goes out intermittently. It doesn't happen when the engine is cold, only after it warms up to the normal operating temperature. Here is a video/sound clip as the car is in Drive with the handbrake on:



About my X5:
It's a 2006 E53 X5 4.8is at 139,000 miles. I always put Shell V Power and change the oil annually. Very recently I've done a full engine overhaul 2000 miles, 2 months ago, The following was replaced - chains, guides, valve stem seals, bearings, coolant transfer pipe, all sensors, all gaskets, all seals, all fluids, 5W40 oil etc. Pretty much a brand new engine and a lot of work done at a great cost. I am gutted that this problem has occurred now after all this preventative work was carried out. The cam shafts, lifters and piston walls were in good condition - pretty much everything was checked while the engine was out!

Before I go back to the garage that did the work, I want to find out if any one has had a similar issue and has found the root cause. I don't want to start doing any work again before I inform myself about all the possibilities.

I've used an automotive stethoscope to check where the sound might be coming from. I doesn't seem to be the water pump, nether the alternator. I do hear the knocking when I touch on the bolts of the valve cover around cylinder 8. From what i've read so far, it doesn't sound like a lifter which is constant and stays with the RPMs?

One thing I haven't checked is the power steering pump, but I don't think i'll hear anything there as the noise in the stethoscope is the loudest on the valve cover bolts around cylinder 8... That worries me a lot..

So, over to the experts... and fingers crossed it is something simple and easy! Thank you!