There is a difference in the diagnosis based on this symptom. A knock that shows up only when hot is more likely to be excessive bearing clearance or low oil pressure or low oil viscosity. Be sure to verify that your oil is not contaminated with gasoline which thins it and allows bearing knock (easy to say, hard to do). Based on your mileage, I would doubt worn bearings unlress you had an oil issue or overheating issue at some time. Since you do not describe the symptom thoroughly, it is harder to go into much diagnosis. This kind of knocking could also be the SC coupler so try giving a detailed description of the symptoms if you need help.

 

hi, reading the last post I'm thinking of this:

I don't remember exactly, but I think the appearance of the knock is time related to the first oil change I made after I bought the car. I'm using 0W40. What if the oil is too thin, allowing for bearing knock and when thee engine warms up the clearances are reduced and it gets better? (even though the hot oil has even lower viscosity ...)

does it make any sense?

What if I try to change tho oil for 5W40?

thanks

 

OK, so almost five years after the initial post the problem is resolved. It was caused by cracked EGR pipe. After replacing it all the symptoms are completely gone.

PS: many "experts" tried to pinpoint the noise, but failed. Finally, when I left the car at "Autobrit s.a." in Geneva, Switzerland, for wheel alignment, when they handed it back the clerk told me: "BTW, I have a note here from the technician. Your car make a clacking sound, it is cause by cracked EGR pipe."

 

Hi!
I'm sorry to be resurrecting this ancient thread!

I'm trying to track down a noise that sometimes seems to be coming from the torque converter area... I thought it was a pulley bearing at first but the closer I get to the bell housing the louder it gets.... its a very low rumble/vibration. worse at idle... Does this sound like the same thing you had with your EGR leak?
Thanks!

 

Would piston slap noise correspond to rpm, i.e., as rpm increases, the rapidity of the knock also increases? My 2006 XK8 has a knock when cold, just started at 47K miles. Stops in 30-60 seconds at idle. A couple people on here told me that was piston slap. Sounds like rod knock to me. What do you think? Richard

 

rod knock doesn’t go away

 

Right, thanks. What problems would cause a similar sound? Richard

 

Do you have the same noise as I do?
Mine is less of a knock and more of a rattly scraping. Sounds like it's coming from the bellhouse while underneath but also from somewhere up top when looking down on the motor... I'm about to start working on the transmission but I'd forgotten about this thread so maybe I'll look at the egr (if I have one!).
It is load dependent and worse on idle - also affected by electrical load like AC or heater...

Ah I just saw you're in Houston? I'm down in The Heights!

 

Did you ever fix it Dickerson ...remember mine had the same with only 3.5 litres of oil in the transmission rather than 6.5 I filled it with.
The piston slap sounds like a bad tappet noise . Mine has gone with 10w40 oil as I noticed it was not present in the winter at say 5 deg C so put it down to the oil being too thin with 5w30

 

I'm in Woodlands/Lake Conroe area. I am no kind of mechanic, but had some experience with cars 40-50 years ago.
Not tappet, not rattle, not tapping, not valve lifters or chain-like noise. A knock. No other way to describe it. A solid, fixed interval pretty loud knock that does not vary in volume or speed with variation of rpm. I haven't ever listened to it with the hood up or standing near the engine, only from inside the car. This happened a couple months ago when we had a few cold mornings.

 

And the point of your comment is ?

 

Location was simply a response to the person who said he lives nearby, and the other information was in response to those that have wondered if the noise was this kind of noise or that other thing kinda noise. Now they know. Sorry I confused you. I hope this answers your question.