Posted on 9/25/2026
An exhaust rattle that shows up when you press the accelerator can be surprisingly hard to pin down from the driver's seat. At idle, the car may sound normal, but once the engine is under load, a metallic buzz or knocking noise starts coming from under the vehicle. Acceleration changes engine movement, exhaust flow, and vibration at the same time. That is why the source can be anything from a loose heat shield to a broken hanger or an internal failure inside the muffler or catalytic converter. The way the noise reacts to engine speed gives us useful clues. Loose Heat Shields Are a Frequent Source of Metallic Rattles Heat shields are thin pieces of metal positioned around the exhaust to protect the floor, fuel system, wiring, and nearby components from high temperatures. Because they are lightweight, a small amount of looseness can make plenty of noise. Mounting points can rust, washers can pull through the shield, or the metal can crack around a fastener. The r ... read more