andy - If I were a betting man and if your mileage is way up there then I would say that the rear axle shafts are probably on their last 50k miles. I have never driven a clicking axle shaft till failure and had a friend that had a mid-80's Camry that finally replaced his clicking CV joints at around 285k miles. The worst thing that I think could happen is they could leave you stranded in the middle of traffic or on the side of the road. You may want to budget for it over the next six months or so.

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Jim