I have changed the gearbox and transfer oil and that has made no difference to the noise ... although the box is a lot smoother
Here is a video of the engine at roughly 2200 rpm, which is where it makes the noise, it sounds ok to me - but i am no expert
https://youtu.be/hWt1iMTIdkE
I will give the 4th and 5th a go next time and out and report back ... thanks for the input