I will do it has driven me crazy for 2 years now will get on it as soon as the weather lets meHey Gareth, sorry for late reply man, thought I got emails when I got replies to a thread, weird. Yeah I literally sorted out the issue a few days ago, however not 100% sure which thing fixed it.
I had the center driveshaft bearing replaced as it was starting to knock, so slight possibility the noise was a knock on effect on a flappy propshaft.
I also replaced the rad shroud and fans, when I took it off I did notice there was slight play in the big fan which the new fans did not have. Also the cabling to secondary air pump wasn't routed very well which may have pushing against the fan at speed, so I sorted that when I reinstalled it. If I were a betting man I'd say fan with play was causing the squeal because it flexing slightly at speed.
Hope that helps in some way! Let me know how you get on.