What type of fuel are you running? Does bumping the octane up to the next level have any effect?

Also keep in mind a lean mixture can cause pinging. Has CEL illuminated recently and/or are there any stored codes? How is timing at idle?

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280