I agree it is nothing to obsess about, but it is not 'korrect.'

Did the tick start after you filled with Mobil 1? If it was there before, due to varnish in the compensator, the Mobil 1 itself might help clean out the compensator.

If it started with the Mobil 1, it might go away when you go back to your usual oil.

If it gets worse, as in it does not stop after a few seconds, you will then need to consider replacing it.

Oh, if I recall, your 420SEL is an 8 quart change, so you'll need 3 more quarts of your Mobil 1 15W-50.

Best Regards,
Jim