Just recently I have been hearing a light knocking sound when I start my XF in the morning. It only happens when the car is changing from 1st to 2nd gear, and it only does it 1 time after 1st start of the day. I also happens after the car has been sitting for a couple of hours. The only consistent thing is that the light klunking sound is happen when the transmission is going from 1st to 2nd gear. any one heard of this a or have an idea what that maybe?

 

I had if for five months, only 1700 miles. Not the kind of knock from cheap gas. It only happens once, and that when it goes from 1st to 2nd gear after initial start of the day. After that the noise never happens again. once a reach my destination and after the car cools down for a few hours, but it only does it once after the start up while going from 1st to 2nd gear. After that the car operate normal. It almost sound like some belt, drive or something going on with the transmission. I do notice that when the car is going from 1st to 2nd there is sort of a strain and slight going from 1st to 2nd gear. Yesterday the check engine light came on, I wonder if the knocking and the check engine light are related???

 

Based on the description, it seems to me the knocking sound is due to ABS kicks-in. Each time when you start the car, the ABS will do a self-test and when ABS kicks-in at the car speedbetween 15kph - 20kph, you will hear a slight knocking sound (sometimes louder, sometimes softer). I have same situation for my XF. My previous MazdaRX8 also have similar knocking sound when ABS kicks-in.My friend who drove Auditold me his similar "problem". Seems thatthis is normal. However, what I don't understand why some other cars such as BMW or Mercedes do not have this knocking sound when ABS kicks-in. I was told that you can eliminate this knocking sound by removing the ABS fuse at the electrical box. But by doing so, you have disabled your ABS. There will be a ABS warning light at your dashboard lighted up.