Total timing in a race car is about 36 deg Max (good starting point anyway). That burning 103 octain fuel. If you are at 34 deg and still have you vacuum and weight systems still intact you could be pushing 40 deg total time. That my friend will burn a hole in you stock pistons real fast.

The reason your engine does not ping at idle or when just reving is pressure. Higher octane fuel resist detonation but increase pressure promotes detonation. A engine with little or no load has much less pressure in the cyclinder because nothing is resisting the piston from moving like the weight of the car.

Flex plate, could be, the sound are very differnt but I have no idea how to explain the differnts. The flex plate has more of a "Tinny" sound to it. Both are simple possible problems and are easy to test. Pop of the dust cover on the torque converter and look for cracks. MOST of the times the crack heads for one of the torgue converter bolts and are easy to spot. After that back off the time like 6 degree and see if there is any change. Dealing with any setup thats not factory you should alway check you timing at the RPM you will push the engine to.