1998 Voyager Blower noise

I'm wondering if anyone can shed some light on this one since I can't find any similar problems via google...

My wife started complaining that she was hearing noises whenever she made a left turn. I took the car out and tried to re-create the problem and couldn't but I did get a very odd noise when I turned on the heater to defrost the windshield. All I can describe it as is a kind of rattling/revving noise that went on for about ten seconds then stopped. I defrosted the windshield, then switched over to the main vents and cranked the heat. The heat was working fine.

The last time something like this happened it was the AC compressor that had died but that was only about five months ago and it was a very different noise (almost a squealing noise) with the accompanying failure of the AC system and a metallic smell coming from the vicinity of the compressor. I turned on the AC and it got VERY cold very fast. I left the van running, got out and leaned in close to the compressor. No smell. What could cause that noise?

Okay, I was able to get a better listen and here's what it sounded like:

I let the car sit for about an hour then started it up again. Again, the same noise. It was loud. REALLY loud. I popped the hood and was able to pinpoint the location to the vicinity of the compressor but it sounded like it might have been belt noise. The first thought was that the belt was wet (it's raining pretty hard around here right now) but after it subsided, again after a very short amount of time, there was no burnt rubber odor and still no metallic odor that would indicate a blown compressor. I drove it around a little, changed the setting on the blower between defrost, heat and AC and everything is still working fine. It's just that god-awful noise at startup.