Ever since we had a torrential rainfall a couple weeks ago, my 06 H2 has been making a knocking noise under the vehicle. I haven't been able to crawl under it yet. The noise is a steady knock, going with the rpm of the motor. It almost sounds like the right side converter but I can't be sure. The noise goes away once the vehicle is warmed up. Has anyone experienced this noise and if yes, what was it?


Thanks

 

I have the same thing in my 03. From what i read it is most likely the broken manifold bolt. Once the engine warms up it goes away due to expansion. At first I thought it may be a lifter or a cylinder but not now since it goes away. Maybe someone who knows can answer for sure. Good luck!

 

When you say knocking, is like a ticking sound or like a true knocking like on a wall sound. Very different but if its a ticking sound I would suspect the manifold, mine has the light ticking but as yours goes away when warm. Ive had a main bearing go out on one my race engines after a build and it is a dull knocking sound, very different than the ticking. Search on youtube at gm v8 manifold ticking and you might recogonize the sound. Manifold bolts are notorious for going bad on them.

 

Yeah mine is the ticking not knocking. Thats why i first thought lifter but after searching this and other hummer forums- im right there with the manifold bolt. Nothing headers cant fix!

 

Unless you are going long tube headers. It is a waste of money as the stock manifolds are basically shorty headers.

 

I haven't been able to pinpoint the noise yet. Doesn't do it all the time. When I have time and I am ready to crawl underneath, no noise. When I have to leave to pick up grandson from school, sometimes noise. But when it is happening, it sounds like something inside the exhaust. When I raise the hood, you don't hear any noise from there. Only on passenger side standing next to truck do you hear the noise. It doesn't sound like a tapping noise like lifters or manifold bolts, like I said, it sounds like inside the exhaust. Hopefully, it won't rain and storm all week like they are predicting and I can look again. Thanks for the replies so far, keep em coming.

 

My passenger manifold had a 3" crack in it. It wasn't visible and I thought it was just the manifold bolts. Both drivers and passengers side had the front and rear bolts snapped off.

The passenger manifold must be known to crack as it seems to be the only one they stock. Look around the bend where all the pipes intersect into one.

 

Well I figured it out. The passenger side converter is coming apart internally. Since it is bolt on, I ordered a converter and the seal and gasket. When the parts get here and I replace them, I will give an update onto how difficult or easy it was. If anyone has already done this, how hard is it? Now I have to spray all the studs and nuts with penetrating oil and pray they don't break. Thanks for all the replies and suggestions.
Now if I can just figure out where the water leak is on my drivers side.


Tim

 

Glad you found out what it was! Should be relatively simple to fix it! Good luck!

 

I had to do the same thing. This job is not that easy, hopefully you don't break the studs. I did and had to remove the entire manifold and then had to drill the stud out. I was lucky enough to not mess the threads up.If you have to remove the manifold, first remove the inside fender and you can get to it a lot easier. Good luck, hope this will help you.