2001 prius: steering column sqeaks in hot weather

The steering column on my 2001 Prius squeaks when it is hot outside. The sound is most noticable when making a turn. My mechanic greased the base twice. The sound goes away, but only for two days then it returns. What is happening? What may need attention/fixing?

Someone else asked a similar question about the Prius last month.

See here:
http://community.cartalk.com/posts/list/185609.page

The car has 99,000 miles on it and has been making this noise since around 80,000. Don’t feel I can reationalize this as a new car sound.

It sounds like a belt is worn. They tend to stretch when it’s hotter outside. I’d see about getting the drive belts replaced.