Hey all, my engine has been pinging on and off at idle only... it sounds as though it is coming from near the alternator ( I dont think the alternator is bad, been replaced not to long ago). I run 93 octane gas and am stumped, retarding the timing does not help either.. has anyone encountered problems like this?

The noise seems to be coming from the alternator (used a screwdriver) but wouldn't it make noise all the time? My car is mostly stock from what I can tell. Previous owner seems to have replaced the mid-pipe, and I have put U/D pulleys and a cold air kit on thus far.