No, not a good sign at all. This is what I meant about hot heads causing pinging. The very first thing I would do is a compression test, followed by a combustion products in the coolant test (you can buy a test kit from Lisle at most good auto parts stores to test this) and/or a radiator pressure test. I'm pretty sure you have a head gasket leak, or a cracked head. In addition, did you have the radiator rodded out? My experience is that just doing the heads leads to just doing the heads again, because most heads fail due to a chronic overheat from a clogged radiator. I'd also check the block deck for flatness. Before pulling the heads, I'd pull the head bolts one at a time, grind a couple of threads off the end, and retorque the heads. Look at FrankR's sermons on head bolt length and cleaning the head bolts holes to the very bottom with a tap. It's VERY possible to get a correct torque reading on the head bolts and never get good clamping force on the gasket as the bolt bottoms in the hole or hits dirty threads near the bottom of the hole.

I'd assume you are losing coolant, too.

Sorry, but I'm pretty sure I'm right on this one.