TEF20 engine knock

[Loftyrules]

Hit a hidden rut a bit too hard with the TEF20 yesterday ran with a slight lack of power so I stopped it but as it idled down it made a slight knocking noise.
Left it overnight and started it up today and brought her back home, power seemed to be back but knocking noise appeared when idling down again. She’s staying put until I can work out what has gone wrong
Any suggestions?

 

[Hair Bear]

This is going to sound daft, and nothing to do with hitting a rut - I have experienced engines running with a knock and down on power when they suffer fuel starvation from blocked filters.