Rattle from under the car at certain RPM

A metallic rattle that happens in a narrow RPM range and sounds tinny is very often a loose exhaust heat shield. Heat shields are thin metal covers held by clamps or welds that can rust or loosen over time, and they vibrate at certain engine speeds.

It is usually not dangerous, but it is worth confirming, because a rattle can also come from a loose exhaust hanger, a catalytic converter with internal damage, or something stuck under the vehicle.

A shop can look under the car and tap the heat shields to find the noisy one. Often a heat shield can be secured rather than replaced. If the rattle comes with a check engine light or a loss of power, have it inspected sooner.