2001 XC70 with periodic 'clunk' in drivetrain

[JohnR]

This car has 169,000 kms and runs very well. After reading your articles, I believe that the transmission module needs to be given some attention: disconnect the auto stop, and determine why it keeps skipping up and down gears in Drive while moving at 60 - 90 km/hr. Manual selection is alright.
However, a couple of times recently while driving along the freeway at about 100 - 120 km/hr the car has 'clunked' in the drivetrain. Not the transmission shifting into a gear, or lockup, but a 'clunk'. Any suggestions what this might be? Thanks