Tie-rod end X2. Had exactly this same noise on the SL. Would make a sort of "pop" noise. The Right-side tie-rod end had completely come apart...how it was even on the car anymore was a miracle. DON'T IGNORE THIS.

__________________
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]