I just had a new thermostat installed a few weeks ago while it was in for a radiator flush.
I'm going to put a new cap on the tank.
I'm hoping it's not the water pump or the radiator itself but I don't know just yet. Gotta try the cheap solution first... ie cap. With that thing singing like it's been doing for so long, and having gotten so bad, I'm going to hope that solves it.
It's going to the shop in the morning so we'll soon see. If I can find a cap locally I may not even take it in if that fixes it. *fingers crossed*
Thanks for the replies guys.