Ultrasonic Range Sensor making a whining noise

Hi,

So I bought a range sensor from RadioShack (3 pins) and it was working fine last night but this morning I powered the arduino and it was making a whining noise. I am just using the code from the Ping tutorial on arduino's site:

/* Ping))) Sensor
 
  This sketch reads a PING))) ultrasonic rangefinder and returns the
  distance to the closest object in range. To do this, it sends a pulse
  to the sensor to initiate a reading, then listens for a pulse 
  to return.  The length of the returning pulse is proportional to 
  the distance of the object from the sensor.
    
  The circuit:
   * +V connection of the PING))) attached to +5V
   * GND connection of the PING))) attached to ground
   * SIG connection of the PING))) attached to digital pin 7

  http://www.arduino.cc/en/Tutorial/Ping
  
  created 3 Nov 2008
  by David A. Mellis
  modified 30 Aug 2011
  by Tom Igoe

  This example code is in the public domain.

*/

// this constant won't change.  It's the pin number
// of the sensor's output:
const int pingPin = 7;

void setup() {
 // initialize serial communication:
 Serial.begin(9600);
}

void loop()
{
 // establish variables for duration of the ping, 
 // and the distance result in inches and centimeters:
 long duration, inches, cm;

 // The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
 // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
 pinMode(pingPin, OUTPUT);
 digitalWrite(pingPin, LOW);
 delayMicroseconds(2);
 digitalWrite(pingPin, HIGH);
 delayMicroseconds(5);
 digitalWrite(pingPin, LOW);

 // The same pin is used to read the signal from the PING))): a HIGH
 // pulse whose duration is the time (in microseconds) from the sending
 // of the ping to the reception of its echo off of an object.
 pinMode(pingPin, INPUT);
 duration = pulseIn(pingPin, HIGH);

 // convert the time into a distance
 inches = microsecondsToInches(duration);
 cm = microsecondsToCentimeters(duration);
 
 Serial.print(inches);
 Serial.print("in, ");
 Serial.print(cm);
 Serial.print("cm");
 Serial.println();
 
 delay(100);
}

long microsecondsToInches(long microseconds)
{
 // According to Parallax's datasheet for the PING))), there are
 // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
 // second).  This gives the distance travelled by the ping, outbound
 // and return, so we divide by 2 to get the distance of the obstacle.
 // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
 return microseconds / 74 / 2;
}

long microsecondsToCentimeters(long microseconds)
{
 // The speed of sound is 340 m/s or 29 microseconds per centimeter.
 // The ping travels out and back, so to find the distance of the
 // object we take half of the distance travelled.
 return microseconds / 29 / 2;
}

Any help would be greatly appreciated. It sounds like there's a large mosquito in my room and it's giving me a headache :(

UPDATE: It randomly stopped the noise and seems to be working fine. Would still love some insight in case it does happen again...

Hi, Never tried using the 3 pin devices, no point the normal 4 pin device is very cheap from China, if you don't mind the wait!! Your code seems to be OK. Is it the U/S whining away, you don't have a buzzer or piezo on board do you?

Check you batteries or power, if low the circuit could e struggling to work!1

Regards

Mel.