What kind of "adjustments" did you make to the IP? If the injectors are original then it's probably time for new nozzles. A metallic knocking noise high up in the engine is usually injector knock or "nailing" from dribbling or poor spray pattern.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]