Intermittantly, our 01 XC70 AWD will make a single "clack" type sound when backing out of a parking space. Once in a great while it will do it when first moving forward after backing up. Closest I can come to describing the sound is what it would sound like if you smacked to 2X4's together lightly. I can only hear it if the windows are down, and it will only do it once. On average I would say it makes the sound about once in every 7-8 times backing up.
Car currently has 61,507 miles on it. I flushed the tranny fluid and re-filled with 3309 about 1500 miles ago. Only issue I have with the car is it still has the Neutral stop thing, but it is the wife's car, and it doesn't bother her. Besdies, I'm reluctant to pay the $165 the dealer wants to download the new software.
Anyway, any advice would be appreciated.
Glenn

 

Could be the brake pads shifting in the caliper bracket.