Thanks so much! Can't believe it was such a simple error! That's what I get for blindly just setting the input into my texture coordinate node!

Thanks Rich, good suggestion. Edited.

lol sorry, I uploaded a version of the file before I added the material. Fixed now, thanks for letting me know.

Thanks, I feel a bit stupid really, seems I wasn't upping the samples high enough. At 512+ it looks fantastic. Thanks for all the other tips too, I'm definitely going to be using them at some point.

Thanks for the great responses. I'm going to try them out soon and will let you know how I go. I've played around with your suggestions on my laptop (where I do my sandboxing) but my main workhorse PC is doing other heavy lifting at the moment.

I'm rendering is 1920x1050.

That's the odd thing here, the renders above were with 256 samples, but doubling to 512 samples looked identically bad... so the old addage of "add more samples" doesn't seem to apply for some reason. I just tried changing my lighting out for a surface emission plane and noticed the noise drastically reduced at even 128 samples! So it must be something to do with using point lights.