Unknown Noise

[Nick2006]

Hi guys, I currently have a 2006 Buick Lacrosse CXL with the 3.8 and recently I have had to replace the notorious coolant elbows with aluminum ones due to one of them leaking on me. While I had everything torn apart I also did valve cover gaskets due to a minor lifter tick I have near the air injection pump. I took the valve cover off just to take a peek to see if I noticed anything loose and everything looked okay so I put it all back together with new gaskets. I went to start it up and noticed a loud thumping/air sound coming right around the air injection pump which was one of the things I had to remove to get the valve cover off. I shut it off and took a look to see if I can see anything leaking or not connected and everything looks to be were it should be. I started it back up and as it warmed up the noise quieted down but still was there. I know for a fact it is not the lifter as it is definitely some sort of air leak or the air injection valve is screwed up some how. I don't currently have any codes from this so its a little hard to pin point were this noise is exactly coming from. I also noticed if I blimp the throttle a little the idle comes down and goes back up to about 1100 were it will sit for a few seconds then make its way down to normal idle. I only have two ideas in mind that it could be, either the valve cover gasket is not seated correcting which is causing an air leak or the air injection pump got messed up when taking it off, or possibly one of the lines going to it. Here is a video of the noise, sorry its not very easy to hear this was in its semi loudest state.

 

[Smith1000]

If I suspect an air leak, I usually spray some wd40 around the area to listen for a change in the idle as a vacuum will pull in the wd40. This can help pinpoint the source. Another way is to use a mechanic's stethoscope to pinpoint the source of the noise.

 

[Nick2006]

I definitely agree it is most likely an air leak of some sort. I'm leaning towards it possibly being the metal line going to the air injection check valve as I had to bend that line a few times to get the check valve out of the bracket in order to take the valve cover off. Ill try your method with the wd40 and keep you updated.