It doesn't ping that much, but I can hear it sometimes. I have been using 89 octane in my 745TI. Last night I decided to try 92 octane. It pings a bit just like before, sounds like rain on a metal roof sort of noise. Is this normal? I mean it isn't constant or anything, just occasionally. Or is my timing too far advanced? After I bought a mechanic checked the timing and said it was ok. Hmmmm.

It could be the knock sensor or carbon buildup in the combustion chamber.
I would start out simple and get a good upper cylinder cleaner like GM uses. Water can be used if you are careful and use a spray bottom to squirt water into the throttle body. Large amounts of water all at once can do a number of bad things to an engine.