Sounds like you might be describing two different things. A high pitched squeal heard when moving at slow speeds, such as when driving through a parking lot, is often caused by an axle seal in the transmission. Because it's buried behind the inner cv joint, it's hard to reach with most spray lubricants. I've had the best luck dousing the area with Mopar Rust Penetrant. Enough will run in by the seal to quiet it for a few hours to a day or more. That will be proof of the cause. The permanent fix is to remove the half shaft and replace the seal. It's about a three dollar part and takes about an hour to replace. A new axle nut should be used when reinstalling the half shaft because it is designed to stretch when torqued. It's a one-time-use nut. Proper torque value is very important to the life of the wheel bearing. The bearing is held together by the outer cv joint and axle nut. The correct torque value is somewhere between 180 and 250 foot pounds. Can't remember the exact value.
My '88 Grand Caravan started doing this two years ago. In typical fashion, I ignored it. Six months ago I noticed it had quieted down on its own. The noise came back a couple of weeks ago, but it doesn't leak so guess what I'm going to do about it?