Yes the ABS speed sensors are in the wheel bearing hub assembly. If the bearings are worn then your sensors are probably not sending accurate information to the ABS system which will cause an ABS light to come on at various times.
I have had to replace the assemblies on both sides of both of my S series vehicles and all 4 times it was accompanied by ABS speed sensor codes popping up.
If the bearings have gone passed the whirring/humming noise when you drive to a grinding noise then you must replace them immediately. I have seen these seize up completely at that point and it ain't pretty.

If you have a clunking noise when shifting from say reverse to drive or during slow speed tight turns like pulling out of or into a parking space, then you may be replacing a CV shaft as well. If a bearing is worn out then the CV is likely not far behind.

 

Thanks for the replys. I'll be going to my mechanic today to see what he's got to say about it. I'll replace what he says on my own. I use him for ideas and only have him fix things in emergencies or when I can't. Wheel bearings are no problem for me, but I've never done a CV.

 

Well I accidentally ordered these:

http://www.am-autoparts.com/AM/Front...1/AM-35913367/

I say accidentally because I never clicked "pay" with PayPal, only "continue." They're what I need, but I know nothing about brand or anything. They do come with a 2 year warranty though. I usually do business with Rockauto, but I could not find the 4 wheel drive wheel bearings.

EDIT: I take that back. I found them on Rockauto and they're more for one of them there than both of these shipped.

 

The reason that there are cheaper as a pair then a single elsewhere could be simply because they do not come with a new ABS sensor. Instead it only has the ABS stator ring that the sensor reads.

The ones from Rockauto likely have the whole setup new sensor and all. If your sensor(s) have been damaged by the worn bearings then you may end up having to purchase a new one(s) separately.