Rapid knocking noise when car warmed up

[vicegrip]

2008 Golf Mk5 1.9tdi 198K miles

Daughter has been complaining of occasional knocking noise on motorway when car warmed up.

It was doing it at a lower speed today.

Here is a recording of it - but done with a phone and not great, however it shows that the knocking is about 7.6 per second and speed would be very appx 40-50 mph: https://files.catbox.moe/d7ioyy.mp3

(In the recording there is a also a slower "walloping" sound very appx every second - unknown origin and not the noise she is concerned about)

Can anyone suggest what the fast knocking might be?

[vicegrip]

The noise became more pronounced and frequent and got to the point where it was too bad to drive.
A mobile mechanic decreed it was a terminal problem with the gearbox.
Yesterday was a very sad day as a longstanding friend was driven up a ramp on its last journey - to the crusher.

[Crasher]