Possibly the blinker itself. This device is sometimes a relay, sometimes a bi-metallic strip. But in either case, its job it to interrupt the light circuit to "blink" the lights (turn signals or emergency flashers).
The construction of the blinker/flasher is usually a thin black plastic base (square or round, where the electrical connectors are affixed) with a metal case (again: square or round...based on how the base looks). Often the noise you hear (when the blinker is blinking) is the relay or bi-metallic strip doing its thing. So this device is usually located under the dash....so they can be heard.
Robi, Dale, and "The Duchess" (lap kitty)
2004 Monaco Diplomat 40' PST
Tow: '08 Buick Lucerne