Moving on 4 or 5 days and the noise is still there, hard to tell how frequent it is as I wouldn't hear it at high revs.
What I will say now is that on several occasions I have heard it when the engine has been cold (but also heard it at full engine temp) and that it sounded like water slushing, like if you move a washing up bowl sideways...
The noise sounds to me like it is coming from just behind the steering wheel area as a guess.
Any ideas please?