If you have Ford Winstar, year 1998 to 2003, you want to call the local Ford dealer and get your rear axle replaced. Ours cracked about 90% of the way through a couple months ago. I went online to do some research before taking it to the garage and found the federal government was doing an investigation on these vehicles. Apparently, the axles have a slight U-shape to them, and in states like ours (PA), where there is moisture and salt on the road most of the winter, this causes the axles to corrode. When these things reach 100,000 miles or so, they have a tendancy to crack.
As I said, we luckily (thanks to my wife's observation of the way the van was riding) caught ours before it snapped, because that can be both dangerous and ruin your tires. I drove my van down to the garage at about 10 mph and got a new axle put in for like $600, which is a lot cheaper than I read some other people paid.
Regardless, Ford issued a recall on these vehicles last week. I called Champion Ford in Erie, and they told me to come in for an inspection and bring the receipt. They said Ford will be sending us a check. Note: I have not heard from Ford yet that there is a recall, I just happened to see the story on-line. I guess I'm saying, don't be afraid to be proactive on this (and you suppedly get a free rental while they are doing the repairs.)