DC Motor doesn't turn and a beep sound is made, also there is a burning smell I was trying to drive a single dc motor with L293D Shield and Arduino Uno

#include &lt;AFMotor.h&gt;
#include &lt;SoftwareSerial.h&gt;

AF_DCMotor motorLeft(3);
AF_DCMotor motorRight(2); 

unsigned char opMode = 0;

void setup() 
{


}

void loop() 
{
motorLeft.setSpeed(30);
motorLeft.run(FORWARD);
delay(5000);
motorLeft.setSpeed(0);
motorLeft.run(RELEASE);
delay(5000);                                                                                        
}


When I turned the power on, a beep sound was made continously. As I was trying to figure out where the sound comes from, I smelled something burning and turned the power off.

I am giving 6V (Four 1.5V  batteries in series) as external power. Burning smell doesn't come from batteries, that's for sure. 

The smell comes from arduino or shield or both. But I think it is the the left LM293D driver.

What did I do wrong? Any idea?
Alright, I finally realized that RPM value was too low. It has to be at least 150 for my case.