This is like the noise you get from an old Ford Pinto engine when the follower is worn from lack of lubrication. A heavy knock at either crank or camshaft speed.

The noise started more a clatter when revved slightly. The engine was quiet on tick-over.

I took it very gently for a few miles and the noise became more apparent and more like a cam follower knock. The noise was such the note slightly changed in a slow cyclic way. (I can't fathom what is going on here) The noise then went away.

Any noise was independent of power. If I coasted then knock was the same as part accelerator.

It then returned with an obvious hiccup to power and was perhaps a little louder.

I got towed home.

I took the rocker cover off, and all the valve-springs and rockers seemed to have their correct clearance. On starting the engine the knock was still present. It's very difficult to locate the origin of the noise but it sounded more top than bottom.

I removed the rocker-shaft so that all valves would be in the closed position. I turned the engine over and I could hear the knock. After a few more turns of the ignition the noise went away!

I've taken the front off and inspected the belts and timing etc, it all looks good.

I did wonder if the crank sensor plate might have been catching the sensor. There were some marks, but that definitely isn't the issue.

Given the above possible misfire on occasions, I'm wondering if this is a pump issue?

What else could it be? Any ideas would be appreciated.

The more I think about the noise and how it changes; I'm starting to think that something has been ingested into a cylinder.

But even if say a blade did come off the turbo, wouldn't the intercooler stop anything substantial from going into the cylinder?

Isn't there a flap for the EGR? Has that been known to coma apart?