The M112 V-6 can become pretty noisy at idle after 1-2k miles
as it breaks in. Without hearing it, I can't tell you if it is normal or not. There have been issues with our M113 V-8's in the E500,
CLK500, and SL500 with noisy motor mounts this year.
The DTB bullitin does not apply to V-6's like yours, but that is not to say you might have the same issue.
Those darn aluminium sub-frames seem to amplify engine noises.
I would let the MB tech specialist they are calling make the call.
He may recommend new engine mounts or just say it is normal.