"Pinging Sound"

[Eh_nigma]

Hey everyone, I'm hoping I can get some advice with what to do with a 3400 thats giving me a pinging sound:

History -
02, 3400 - 120000KM on it, buddy called me up said the engine "blew". Took it down to the heads, No. 6 cylinder area was warped (determined this was due to cristalized dexcool in the coolant vessels). We had the heads redone, all good to go. Put it together, had a banging sound that eventually went down to a subtle clicking sound.

Tried thinner oil, tried thicker oil. When the engine is cold, no pinging sound. When it warms up, it's back. Same place, right around the No. 6 cylinder. Took the heads off again, retorqued everything to the specks that were given for the 3400... can't get rid of it.

Engine works fine. Loads given, taken from slow idle to a steading increase until the governer kicks in, no damage is being done, no power is missing, just keep getting that constant pinging sound.

Any advice?