Occasionally when i rev match a down shift i jab the throttle and sometimes i hear a medium volume (ie. it's definitely heard with the windows down, and more felt than heard with them up) "POP" from forward of the cabin. I've been told its detonation. I originally thought it some sort of backfire. I am on a stock chip and run 93 octane religiously.

I have had the problem before doing any thing to the intake. When i remove the oil cap while the motor runs the engine does not bog down. This is a sign of a vacuum leak that I am unable to resolve after many hours of checking everything. One friend told me that the intake manifold gaskets can go bad. I am not sure, i haven't pulled the intake manifold. Whatever this POPing sound is, i really really want it to go away because it sounds not good.