Ugh. Water pump pulley replaced, another belt tried, the noise still remains.
Remove belt... noise seems to be gone.
Just to reiterate:

(All Mercedes brand parts)

New:

Alternator
AC Compressor
Belt Tensioner
Idler Pulley
Viscous Fan Clutch
Water Pump
Water Pump Pulley
Serpentine Belt

The only thing that hasn't been replaced is the crank pulley, but it makes no noise and is not wobbling with the belt off. Interestingly, if I turn the headlights on, therefor putting a heavier load on the alternator, the noise seems more consistent. Again, it made the same noise with the old alternator as well.

Hair pulling coming in 5,4,3,2......