knock
 

Every once in a while when I start my engine after it has sat for a few hours I here a loud knock noise. I reported it to the dealer a while back, 9 months, and they never could hear the noise. Today my dad heard the noise and thinks it is internal, we think it could be a rod in the engine? He owns an auto parts business so he knows what he is talking about. Have any of you guys ever had this same noise? :dunno:

“A loud knock noise” is too vague to diagnose, but it could be a hydraulic lash adjuster which has collapsed causing a knocking (tapping) at start-up but that re-adjusts a few seconds after it receives oil pressure, or it could be a wrist pin, rod, main bearing or some other reciprocating part within the engine.

Several years ago I had a Mazda van which when the engine oil had about 2,500 miles on it several of the lash adjusters would collapse causing a tapping noise for several minutes after start-up. Within 100 miles after changing the engine oil the lash adjusters would again function correctly.

Additionally, also with the Mazda, it developed a knocking sound that I would have bet my life was either a failed rod or main bearing. My mechanic son-in-law, who also initially thought the same thing, put his stethoscope all over the engine and determined that the knocking was coming from the power steering pump. I replaced the pump and the noise was gone (the power steering pump is a “vane” pump, and I still don’t quite understand how it was making a very loud knocking sound).

So, your knocking sound is going to have to evidence itself to a mechanic which may be problematic (you might consider tap recording it for play back to a mechanic).

Thanks for the idea. My X is still under warranty so I plan on just driving it until it quits. I know that sounds bad but since they can't find the prob now maybe they can when it quits. :rofl:

Has your problem been resolved, because I am having the same issue with my 4.4 which is out of warrantee.

Did any of you guys figure out what this was? I'm now starting to hear this as well. Just after the truck has sat for sometime.

My 4.6is does it in the morning on first start.....around 50% of the time.

50K miles, not really sure what to think about BMW.

My 2003 4.4 use to do it on start up also. Was never an issue.