I have an 04 limited 6 speed manual XF that is a little bit rough sounding at idle.
When I'm at a stop light or just pulled into the garage and shift out of gear and let off of the clutch, then I hear a faint noise almost like knocking, but when I depress the clutch it's smooth as butter.
I did do a sanity check and tried this with the emergency brake engaged and then with it disengaged, same result both times.
There's no fluctuation in rpm idle, it stays right between 5k and 6k rpm.
I'll be replacing the air filters this evening with K&N.
Does anyone know what this could be and is it something to worry about.

Any help with this would be greatly appreciated.

Update: K&N air filters installed, oil changed (mobil 1 - 0w 40), K&N oil filter installed.
engine is running smoother than ever(while driving), but still have the noise when I'm stopped with the car out of gear and the clutch disengaged.

 

I too have noticed this with my 2004 6 speed manual XF. I only notice the noise when i put the car into neutral and the engine is idling and just as you said the noise goes away when i put the clutch in.

I have since changed out the original spark plugs and fuel filter (last friday) and have not noticed the strange noise since. My guess is that one of those components was causing the engine to idle to low and the clutch didn't like it.

 

Possible throw-out bearing; could be normal depending on how loud. Trany parts stop rotating when you put the clutch in. Therefore, you will stop hearing your drive gear rotating. Now, If the throw-out bearing is bad it will often wine or grind.

Probabily just rotation, correct me if I'm wrong (anyone).


P.S
First post
Glad I found this place

 

Thanks for the replies. It's not very loud at all. In order to hear it, I do have to turn off the vents and radio and lean forward, hopefully I'm just being paranoid about it.
There is no whining or grinding noises.

 

You might reduce that 5000 to 6000 rpm idle. Noises are common, try opening the hood to get a different perspective and localize the source a bit better. Woody

 

I have 128k on mine and I've noticed this same slight 'knocking' sounds that sounds similar to a diesel engine. It's always bothered me...but I'm glad to know others get it to and still seem to run fine. I only notice it at idle and under 1k RPM, or when it's really cold out. I heard a C320 recently that was making the exact same noise (except much louder), so its like others have said around the forum, it appears to just be a noisy engine.

 

I am curious though, what rpm does everyone else's car seem to idle at? Mine is steady, but drops to 500rpm sometimes and that just seems low... but again, if they're all doing that, then its fine by me.

 

cant help the OP.... but my Aero idles at 500-700rpm....depending on whether I am in park or drive... yes, it's an automatic....

 

.5k to .6k would be fine as an idle speed.