Why does my van make a moaning sound when I turn in the rain?

The belt might be getting wet and slipping.

What belt are you talking about, the serpentine belt? Is there a way to prevent this belt from getting wet?

Not really, but if it is the belt look toward tensioner not holding belt tight enough. Belt should feel fairly tight when pushed on.

I don't think that it is the belt, I just had it tightened a few weeks ago. I recently had to replace the rack-n-pinion and I am wondering if it has to do with part of the steering assembly because the van only "moans" when I turn the vehicle. Although this sound occured before the rack was replaced also.

Most rack and pinions will make some noise as the seals move back and forth in the rack tube as you turn. It's really hard to say without hearing it up close and personal.

The "moaning" sound sounds like if you were sick and were maoning because your stomach hurt. (that's the best way I can describe it :) ) It sounds like the van is complaining during every turn. It doesn't sound like metal grinding, just a "rrrrrrrrrrr" or "mmmmmmmm" sound. That's the best I can do in describing the noise.

Possibly ball joints, tie rod ends.......try to have someone listen under or around car while you turn the wheel maybe can narrow it down. Otherwise thats a hard one to say without being there....

If you have run flats, it could be your tires....