timing, dwell + strange noise!

[RyanH]

Hi all. Could anybody explain a noise I have in my engine, 1970 911T? I'm going through setting the timing and dwell then onto the carbs and mixtures etc. The timing is running forward (approx 2 o'clock position) and fast at the moment, about 1100. When I drop it down to between 800/900 there is a sporadic ping and a low grumble coming from the bowels of the left hand side of the engine. Hard to explain in words. I guess my question is could this be something to do with the timing being forward and fast? When the car is warm and running at 1100 the noise goes away. I'll find out when I adjust everything but wondered if anyone had any ideas?!