My XF started tapping on cold start-ups about a month and a half ago, and it would go away after a minute or so. I had the oil changed right after it started because it was about time for one, but it continued. The good news is today I started it up and it was pretty quiet for some reason. I left it sit for a few hours and started it up again and it was still pretty quiet. It has 14k miles on it right now. I don't know why it would just go away, but hey I'm happy lol. I think my car knew it was in trouble or something because I searched on Benz forums like non-stop the last couple days about noisy mercedes engines, and now the noise goes away.

Another thing... A few people had an engine that would have a ticky sound to it on acceleration, but be quiet at idle like mine. They discovered something about getting some bushing installed in one of the motor mounts and the noise would go away. That is something I'll have to keep searching.

 

I have almost 47k miles on mine and I almost always get ticking for a second or two when I start it up. It's more noticeable after the car has been sitting overnight. This is pretty normal for a car with hydraulic lifters from what I have seen since they bleed-down a bit when the engine is stopped.

 

It's not for a second or two it's for a minute or two. It did it again today though when I started it. I was hoping it would be quiet again. It's fine when it's warm.

 

I just started noticing about 3 weeks ago that mine is noisy too. I have 68,700 miles on mine. But its not that normal hydraulic lifter tap its actually a chater like sound for about 5 minutes and when I start to drive as the RPM's go down it will chatter. Does it for about 10 minutes total and as the temp gets to average it quits and wont start tapping until the engine cools down. It's going to my "5 star" dealer this morning. I hope its not an arm and a leg...

 

I notice mine doing the noise at startup about a month after oil change. I tried GTX synthetic oil, but I think i'm going back to the Mobil 1 on the next oil change. It just harder to fine the 0-40.

 

If you are not using 0W-40, it will do that. The oil takes too long to circulate on a close tolerence motor and would not run anything other that that for several reasons.

 

I had the same issue for a while but in the past week it sounds more like an engine knock. I have seen the check engine light come on in other cars and usually changing the plugs made it disappear. My car does not have the check engine light but the knock really starts above 2000 rpms and is pronounced now. What used to sound like the problem described in this post has become aweful sounding and I am tentitively taking it in to be fixed.

 

That's another reason I use AMSOIL 5w-40 which is just a little more thicker than the 0w-40 which does make a difference. 0W in forced induction cars is not my cup of tea. I had the same problem with my turbo GTI and the heavier weight oil did make a difference with that car also.

 

I have been a long term customer of Amsoil but I am not going to use the 5W weight. When I bought my car, it was from a dealer and they just did an oil change but put in 5W. Mine would tap upon start up for a about 3 to 5 seconds, then go away. I changed the oil to Mobil 0W-40 and it went away and has not done it since which is about a year and a half. I guess it depends as to what the issue is but mine was certainly due to the oil not quite getting to all the areas as quick as the 0W.