Man ... that's a weird head gasket symptom. I was going to guess that the thermostat had come apart, or something. Good to hear you got 'er ironed out, though. Congrats!
Never heard that noise in all my life, a few pro-5.0 guys stated the same hting, wierd ****, let me tell ya....It was the back coolant holes on the H/G that were not able to allow coolant to pass being they were blocked off/on bacwards-causing isolated overheating in the head-Whicwas the noise itself. Dude-the coolant actually started to burn through the gasket itself and you could see the shiny metal of the H/G-it was like pounding it-Unbelieveable ****!