One problem related to rear suspension springs has been reported for the 1998 Toyota Avalon. The most recently reported issues are listed below.
Rear springs/struts are so weak that if I have two people in the back seat, or several suitcases in the trunk, the rear suspension bottoms out. This causes a very uncomfortable wiggle when it comes back up. My new tires are starting to flat spot as did my last set. I brought this to courtesy Toyota when it was under warrentee. They claimed no problem and readjusted my headlights. I have contaced capitol Toyota in chatanooga, TN. A couple of times. They said they have had several complaints about this but couldn't do anything about it unless something was worn or damaged. I called Toyota. They said the same. But took my name and said that if enough people complained they might address the problem.