Don't like that noise!

That works!
I don't know about the 2.8 M52, but my M54 3.0 had a knackered fuel tank vent solenoid (situated at the front of the engine near the power steering reservoir). I bought a new (cheap) one and that makes a very similar noise on tickover (it doesn't run all the time but a lot at tickover). It's either that or tappets IMO.

I thought mine was a noisy tappet, but when I unplugged the new vent solenoid it stopped, so I know it is that.
 
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