I suspect the bad head gasket, cracked head and/or cracked block caused the freeze plug to let go by letting compression into the water passages. I would go farther and say that the bad head gasket caused the freeze plug to let go and the resulting overheat caused the head to crack and maybe the block too. These blocks don't crack very often. You might get them to warp if you get them really really hot. I half suspect this might be your problem. You need a machinists straightedge and some feeler gauges to measure it.

Chasing the threads is good, but you have to also blow them out with compressed air or something like brake clean to float the grunge from the bottom of the hole. Chasing gets you clean threads, but if the bolts bottom out before properly torquing the head, it is for naught.

As for the sound, I don't know. It might be a problem, it might not. I do not know. It could be something like the check valve on the AIR rail over the exhaust manifold.

As I said before, you need to put some man made pressure into the cylinders so you can see where it comes out. It can exit the block, enter the coolant passages or escape into the crank case. Spinning the engine will not tell you where it is going.

What compression numbers are you getting?

Michael