Thanks for everyone's help. It does appear to be a noise coming from the belt. I half-heartedly spayed on belt dressing and the noise mostly stopped.

This did not sound like the belt squeals I've heard in the past. For future trouble-shooters: The video/audio file picked up the true sound fairly well.

__________________
Neil
1997 E300D - naturally aspirated
280,000 miles (as of November 2015)