Just thought I would update everyone.
Mercedes Benz NA 800 number (Hanora) has no explaination as to why the oil pump relief valve will not fit my oil pump.
Neither does the Charlotte Dealership.
Since they would be unable to return the oil pump once they opened it up to determine if the relief valve would fit, they refused to do so.
The only solution (per Mercedes) is to replace the oil pump in my car ($268 for the part).
If it works, that would be a relatively inexpensive cure. But they would not guarantee that replacement of the oil pump would solve the problem.
In the interim 2 weeks, the noise has again dissappeared.
I have considered just buying the oil pump and keeping it in the trunk as some sort of voodoo protection to keep the racka-racka monster away...but not yet.