Haven't had this fixed yet but just wanted to say I figured out what the squealing noise was!
It's water/steam escaping from the gap where the hose has split and a temporary repair has been made. That's why it only happens when the engine has warmed up and stops when the whole thing cools down. Basically when the engine gets up to temperature, the water I'm currently putting in the car until I get it fixed is heating up and boiling off I guess and escaping through the hole. The flapping tape around the hole is causing the change in tone of the noise. Checked it this morning by putting something around the area and trying to clamp it (not easy when its super hot!) and the noise would change or stop depending on how I covered it.
Will have it fixed tomorrow and then drained and replaced with proper coolant/antifreeze.
Thanks for your help everyone!