My replacement N900 has arrived. Got a few days before I have to drop my old one back in the mail so will do some testing.

I can already say in my case the charger has nothing to do with the issue. I used all the accessories that came with my broken N900 on the new one without any issue. Mic works fine on the new unit. All of my audio settings / loaded drivers etc seem to be consistent on both units. Not seeing anything out of the ordinary yet. More playing tonight - now just having fun re-configuring the device.