My 2008 Seat Ibiza making strange knocking noise

Hi everyone. Alright so I've recently bought myself a second hand Seat Ibiza 200 1.4i model. Only issue is that there seems to be s trance knock on the front side of the car whenever I put the car into reverse and then lock the steering to the left. My initial thought was that it was the CV joint, but it's not a repetitive knock. It knocks once and then it stops. It sounds as if something is hitting the brake disk, and it's a little hard for me to pin point the problem. Any ideas on what the issue might be?