the signs of pinging are, well, pinging. pinging is the sign (of detonation, preignition, etc), not the cause.
if you want the possible causes, there are many. most often, it is too much timing (for the grade of fuel), too low an octane of fuel, artificially raised compression from deposits, running too hot, hot spots in the chamber, wrong plug heat range, and so on. if you search, Jrichker has a pretty nice list of all the causes.
if you were running fine, and now notice pinging, not knowing anything else, i would back the timing down. i just did that yesterday, when i noticed some. in the winter, i run 14-15*, and in summer, i run 12*. we have been at about 100*, so i knew the time to back it off was coming.
good luck.