This was like something rattling below the windshield, behind the dash. It did not seem like it was coming from under the hood. It even did it at idle. Like I said, HUMMER had a service bulletin out on it, so it must have been a common problem.....at least with the Alphas, anyway.

 

when i had the 3.7 while towing up hill, and the engine was really working, something would start banging around the firewall area. didn't sound like bolts in a can. i never figured out what was going on and it kept running. later, i saw something about the hoses-through-the-firewall issue. that's what i think it was. now that i have the alpha i guess i should get a couple zip ties... random thoughts.

 

I have an 06 H3. I have been trying to figure out the noise too. It only happens when i get the rpm's around 2000 from a dead stop. I read in other post about the heat shields. Took them all off and the noise was still there. Zip tied the heater hoses. Pretty much tightened anything loose. But i still have the loud metal rattle noise. I have read on the GMC Canyon post that they had the same issues with the balance shaft. That the chain is loose. Anyone have this issue on the hummer? Considering it shares the same engine platform.

 

Are you guys describing a sound that is something bumping around or engine knock kinda sound. Sounds sort of like some of you described how and when that occurs. If so either your not getting the proper octane at the pump for some reason or your knock sensor is bad or needs to be reset.

The Alpha heater hoses have a click lock at the firewall and my came off because it was not fully engaged. Caused some weird problems.

 

I had this "rattle" on the passenger side around the tire area is where it sounds like it was coming from about a year ago. I Took it in to my dealer and they said it was the head. Kept it for 2 weeks and now about a year and a half later the "rattle" is back..

 

I think they're talking about more of a rattle than a clunk. I've got the same problem on my 06 H3. I'm going to check the heat sheild and heater hoses tonight, as well as a few other things. I'll post if I find the problem.

 

Didn't read the whole thread, but there is a GREAT chance that it's the intake resonator (the part with the Vortec writing on it on top of the motor). That can be fixed a little by tightening down the clamps, or eliminated altogether by getting an airdoc intake

 

I ended up taking mine to the dealer for an opinion. They think it's the manifold heat shield, but I took it off and the noise is still there. I've also tightened everything I could find. It's definitely a metal on metal rattle, not a clunk like some people have stated. Same thing, taking off from a stop and moderate acceleration. Once the rpm's are brought up it goes away.

 

2007 Hummer H3, I do some off-roading. I had a rattle noise under the passenger side, turned out the transfer case guard was bent up touching the transfer case, I took the thing off, welded a new guard out of 1" square tubing that stretches across the frame cross members to protect the transfer case. The new guard works better than the factory one.
The factory guard is a stamped piece of maybe 1/16" steel and is bolted on the front frame cross member with 3 bolts.

If anyone is interested in what I did or needs some help let me know.

 

i have an 06 h3 with about 75k on it....mine sounds like a metal vibration on the passenger side in the front....almost like a skid plate is loose and vibrates on the frame but only at low RPM's. dealer thought it was the heat shield but they are removed and still have the problem. does not do it while sitting in the driveway, only when moving, which makes it a pain to figure out.