I know this is a long shot, but I'm trying to ID a noise coming from the front of my 1995 Grand Caravan.

Essentially, if you keep your mouth closed and make a low "mmmmmmmm" sound, and raise and lower the volume in a cyclical pattern, that's the general idea. The pitch of the sound remains fairly constant, but the resonance varies. It's more noticeable (intense?) at highway speeds, but is present at all speeds. The noise is accompanied by vibration that can be felt in the floor (also cyclical). It might cycle anywhere between 1/2 second resonance up to 2 or 3 seconds.

Can't really tell if it's driver's or passenger side (kind of like the non-directional bass from a sub-woofer). I originally thought it was my driver's side wheel bearing. I replaced that (it was old and rusty). I also replaced both strut assemblies ( they were both completely shot). I then got an alignment. The sound lessened a little for a day or two, but not anywhere like I thought it would, and now it's back with a vengeance.

The sound is not present when idling or when stopped, so it's not an engine noise. I took my boss for a quick ride. He works on cars alot. He couldn't identify it.

 

I would venture to guess that it's either the other wheel bearing, or the one you replaced was junk.

There is also the possibility that a tire is out of balance or out of round (yes this happens).

I would start with checking the wheel bearings.