That's a great question that gets to the heart of everyday urban soundscapes! The difference in noise level when emptying a metal versus a plastic trash can is quite significant, and it boils down to the fundamental properties of the materials.
When a metal urban trash can is emptied, it typically produces a loud, sharp, and resonant clang, bang, or rattle. Metal is a highly resonant material, meaning it easily vibrates and amplifies sound waves. The act of lifting and dumping it into a truck causes the can itself to strike against the lifter or other surfaces, creating a piercing noise that can carry quite a distance. It's often described as disruptive or jarring, especially in the early morning or late at night in residential areas.
In contrast, emptying a plastic trash can usually results in a much duller, softer thud, scrape, or muffled rumble. Most modern plastic bins are made from dense polyethylene, which is a non-resonant, dampening material. It absorbs vibrations rather than amplifying them. While you'll still hear the sound of garbage bags sliding out and the bin being set down, the plastic itself doesn't "ring" or create that sharp metallic percussion. The overall acoustic profile is lower in both volume and pitch.
From a practical standpoint, this means plastic bins generally contribute less to noise pollution in dense urban settings. For people living near collection routes, the shift from metal to plastic cans can mean a noticeable reduction in disruptive morning sounds. However, it's worth noting that the loudest part of collection often comes from the truck's machinery itself, but the bin material plays a key role in that initial, distinctive emptying sound. So, while neither is silent, the plastic option definitely offers a quieter "thud" compared to the iconic "clang" of metal.