This topic was discussed here before (long time ago), but wondering if anyone has taken their XF in for repair on this issue.

from what I hear, the knocking sound is due to ABS kicking-in at low speed (10 to 20mph). Each time you will hear a slight knocking sound. I also heard, this is a normal operation?

 

Many cars have an ABS self test that happens the first time you exceed ~15mph on a journey. I have had one or two German cars where this can be heard. So it could be a feature rather than a problem.

 

It should happen only once shortly after moving off for he first time after starting up.