Thanks folks, for all the excellent tips. I removed the spare tire from under
the van, luckily it is in excellent shape, with alloy wheel just like the
rest. I replace the front tire first and took a short drive every tire
change. It was the driver side front tire after I replace it with the one I
removed from the passenger side, the problem disappear. I found the tire wear
close to the inner wheel was uneven, but nothing else suspicious. I assume
that must be it. Thanks again.

Albert