One problem related to front suspension hub has been reported for the 1999 Hyundai Sonata. The most recently reported issues are listed below.
I noticed my left front suspension on my 1999 Hyundai Sonata GLS squeaking loudly while driving city speeds. My mechanic noticed rusty area around suspension control arm, etc. Labeled it as a priority repair for safety reasons. I previously had the complete rear wheel hub replaced because of corrosion a few years ago, too. I have not gone to a Hyundai dealer yet so I'm not sure how to proceed from here.