Doesn't sound nice at all.
Just for grins....check to make sure the fan isn't hitting the bottom of the fan shroud. (This can happen if the engine mounts decide to go flat rather quickly.)

****, that sounds exactly like when my fan was eating my shroud.



Check the caps on the end of the motor to make sure they are not hitting the fan.

I had the same though about the fan but was too embarrassed to suggest it. Glad I'm not the only one that thought of that. What about the low oil pressure though?

Well...not sure how excited I would get over the low oil pressure....he did say it was about to overheat, and with it that hot, and idling, there isn't going to be much over 1/2 bar of pressure.

Main is a dull thud,rod is only apparent generally during acceleration or load.

Sounds like plastic,look for what the others here have suggested.

Well its none of then fans (the two ones in the front) and the metal one behind the radiator is it? i dont know, but its not a fan, it does sound like plastic. if a piston were to be slapping (what is a piston slap) would it make that much noise and sound like plastic?

Do fans go faster under acceleration?

Check the metal one with the engine off. If there is contact, it may not necessarily be with each fanblade, so rotate it all the way around to be sure.

Yes, the metal fan would increase with engine speed, as it is physically connected to the engine (unlike the electrically powered fans up front)

yeah its not that...

E420 is sold.