Hi lane, I'm with Klaus. It is probably one of the front hubs (bearing). When you can hear it at driving speed, It's pretty bad and you should get it fixed quick before it does more damage. I've had to do both of mine. They can sound like a bad tire when they go. I did one shortly after noticing the noise at low speeds, The other side gave out a few weeks later but I let it go till I started to hear it plainly at driving speed. That one was much worse, being nearly frozen when trying to spin it by hand and it had gotten so hot it turned partially blue. The axle shaft had also just started to show a tinge of color as well. I think I got it just in time. It can be hard to tell which one it is but if you (and maybe a passenger) listen carefully you can usually get it right. The hubs were about $135 each (Timken) at one of the discount car part internet sites. FCP Groton might be similar or even cheaper. It's not a very difficult job if you do your own work. I didn't have to remove the steering knuckle (on a 1999 S80). I think I described the job here, do a search on "s80 wheel bearings" or search the posts for 10/07. The last post in the thread describes how I proceeded. Note that on my early 99 S80 there were no seals/dust seals, yours may have them. Oh, I'd have to add that I bear no responsibility if using my described method doesn't go well (or ends up costing you more)!