I have a 2008 h3 with 51000 miles on it when i start it up cold it makes a rattle or rumming noise took to a dealer today and they said that they are not sure what it is they will try again tomorrow to figure it out any ideas thanks

 

Mine was doing that and it would stop when it warmed up. It turned out to be a very large crack in the exhaust manifold . The raddle was the exhaust gas hitting the heat shield. The manifold is part of the emission warranty . My H3 had a little over 70k on it and was still covered.

 

ok its been a long day that should have read rattle not raddle sorry.

 

Exhaust heat shield rattle when cold is a common problem - look for missing or loose exhaust heat shield bolts.

 

would this happen only at certain RPMs? I have something similar that only happens until the '06 warms up a bit. It only happens at or around 1000RPMs (whether idling or in motion). A very annoying, loud rattling sound. After the car is on for a minute or so, or at RPMs other than 1000, it is perfectly quiet. Any ideas??

 

Mine does the same thing, I have an 07 just hit 70k and this noise is driving me crazy, so I should check out the heat shield or look for a crack in the manifold?

 

Ok mine stopped making that rattle after the dealer replaced my exhaust manifold. Now that everyone is talking about their rattles , mine started again and IT'S LOUD !!!! When I pulled in the driveway and stopped, it stopped. I looked under , over , in front , behind, nothing . I drove around the block and it rattled again. Now it's time to just park it and start touching everything I could find. Ok I found it , it's the heat shield over the right motor mount. I pulled it up a little and now after a 4 mile road test NO noise. I hope this works for you too.

 

it vibrates at a resonant frequency

 

If it's like mine was , it's pitch/tone will change with rpm's ... You don't have to move the shield very much , just get up off of the motor mount a little... It's a 30 sec fix . I just drove 20 miles and no rattle .