When revving the engine on a steady rpm, the rpm drops a bit after every couple of seconds an after releasing the throttle the engine idles for a bit an then also a drop in rpm is heard at which it will keep idling.
I have recorded the sound with my iPhone:
https://gofile.io/?c=Przdft

I have had starting issues with it which are not completely gone but that is in another topic:
https://www.landyzone.co.uk/land-rover/td5-does-not-fire-up.355951/page-2#post-4775810