2006 Buick Lucerne Q&A

2006 Buick Lucerne Question: What cause a knocking noise 5 to 10 minutes after first start in the morning?

There are three metal knocks, in quick succession, resembles radial tires going over a crack in the road. Happens as fast as you can read knock, knock, knock. It is solid sound, not a tinty and nothing else happens with the engine. No hesitation or drop in RPM. -
Answer 1
car needs to be looked at to determine noise -
Comment 1
First of all, I have checked several responses from you on this website and you rarely give advice except for something similar to what you posted here. Second, I checked with the Cadillac forum (same engine) and found out a service bulletin for this problem. It states the knock is caused by the engine heating up before the cadalitic (spelling ?) converter. The system is programmed to puff 3 to 5 hot blasts into the converter. It says it will sound similar to what I stated in my question. -
Answer 2
This is common for most engines when first started after sitting for a period of time. When a engine sits not running the oil drains back down to the bottom. When it is started the engine takes a second to pump the oil from the bottom back through the lifters in the top off the engine block creating a ticking or knocking sound. Adding a quart of Marvel Mystery Oil helps with this issue, find it at auto parts stores anywhere. -
Comment 1
I checked with the Cadillac forum (same engine) and found out a service bulletin for this problem. It states the knock is caused by the engine heating up before the cadalitic (spelling ?) converter. The system is programmed to puff 3 to 5 hot blasts into the converter. It says it will sound similar to what I stated in my question. -