Hi Ian, as a recently member who has just bought an 2011 XF 2.2D facelift, I have noticed an very intermittent high-pitched buzzing noise from the centre speaker near the windscreen. Sometimes is lasts for a very short period, and sometimes longer. I found a short clip on YouTube which seems to replicate a similar problem in a Jag (but not XF) coming from the same area: https://www.youtube.com/watch?v=uoTnDOibDzY
Your instructions of how to fix are amazing, but would you be able to confirm that this is the same problem you experienced before you applied the above technique to eliminate the problem?
Many thanks, Andrew