OP says noise goes away on a diesel purge.

Your video makes it hard to hear what's going on because the aux fan is running. Can you make another one with the A/C shut off and that fan not running? You might get better help that way.

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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]