So after giving the transfer tube a good clean, making sure it's lubed and hand tightening.
Got a bit of an update.
A) I aired the marker and the leak began after about half a second the squeal started, I fired the marker and the squeal increased it's pitch even higher, however this time it felt the leak and the squeal was coming out the back of the reg.
B) About an hour I tried again, I hadn't changed anything or touched the marker, however this time when I aired, the leak was smaller, again coming out the back of the reg. Upon firing the marker the squeal started, firing a second time the pitch got higher.
I've got a video of the second time I tried (It's not a pretty noise.....)
https://dl.dropboxusercontent.com/u/77545216/Axe leak 2.mp4
The problem just seems to be moving about the marker as time goes on, I've been told that maybe it's the temperature but surely a bit of cold wouldn't make it sound like a wounded animal?