2007 Hummer H3 Base 5 Cyl 3.7L
Transmissions & Drivetrains
Loud annoying metal rattle under truck.
It sounds like a heat shield for the catalytic converter but I'm not sure. This rattle happens ONLY between 15mph and 19mph. At 20mph it's totally gone. Also it rattles between these speeds whether your accelerating, decelerating, coasting in gear or even in neutral. It must be some sort of shield but maybe someone else has had something similar so I figured why not throw it out there and ask. Any clues???
It sounds like a heat shield for the catalytic converter or the honey comb inside the cat. If it is the cat, this vehicle is still under the warranty for 8 years or 80 K miles.