The CV boot on both front axles were split and or leaking, and we were hearing a clunking noise from the passenger-side wheel when we stopped, so we replaced the axles. For the record, it didn't help the clunking noise, but at least we fixed a known problem before the axles just fell apart on us.

We ordered the axles from Raxles (http://www.raxles.com) they were $294.75.