Yeah i forgot about the diff bearings..It could also be the pinion bearing going or like they said earlier,could also be the tranny..I would just give the whole drivetrain and suspension a once over..When my front wheel bearing went it gave no warning signs..After a 20 min drive and pulled into the gas station i got a nice clunk and then all grinding..Luckily i didnt ruin the spindle..You cant forget shes 20 years old..Plus probably not taken care of all that well..

How much weight do you carry on the average? I'm asking because I just picked up my mom from the SFO and took her to Travis AFB in California. It's a 70 mile trip and after a while I noticed a whirring noise coming from the back. I usually drive alone and remarked to a friend that my car doesn't like 3 people in her. The manual says she has a load cap of 750 lbs. With luggage, my mom and I, I think we were getting close. After unloading. I drove another 40 miles to Emeryville and had no noise. I hope this helps.