Collision Avoidance Robot making beepy noises?

hello all,
so here have pretty basic collision avoidance robot:

code: [select]

#include <servo.h>
#include<afmotor.h>
//declare servos
servo scanservo;     //ping sensor servo
const int motor1 = 12;
const int motor2 = 9;

const int steer1 = 13;
const int steer2 = 8;

const int = 800;
const int turntime = 500;  //number of milliseconds turn when turning
const int pingpin = 4;     //pin ping sensor attached to.
const int echopin = 5;     //pin ping sensor attached to.
const int scanservopin = 7;   // pin number scan servo
const int distancelimit = 10;   //if gets many inched from
                                 // robot stops , looks go.
                                 


//setup function. runs once when arduino turned on or restarted
void setup()
{
  serial.begin (9600);
  scanservo.attach(scanservopin); // attach scan servo
  pinmode(motor1, output);
  pinmode(motor2, output);
  pinmode(steer1, output);
  pinmode(steer2, output);
 

  //variable inicialization
  digitalwrite(motor1,low);
  digitalwrite(motor2,low);
  digitalwrite(steer1,low);
  digitalwrite(steer2,low);
  delay(2000);        // wait 2 seconds
}
void loop(){
  go();  // if nothing wrong go forward using go() function below.
  int distance = ping(); // ping() function see if ahead.
    if (distance < distancelimit){
    stopmotors(); // if ahead, stop motors.
    char turndirection = scan(); //decide direction turn.
    switch (turndirection){
      case 'l':
        turnleft(turntime);
        break;
      case 'r':
        turnright(turntime);
        break;
      case 'b':
        backward(1500);
        turnright(1500);
        stopmotors();
        break;
      case 's':
        forward(turntime);
        break;
    }
  }
}

int ping(){
  long distance, duration;
  //send pulse
  pinmode(pingpin, output);
  digitalwrite(pingpin, low);
  delaymicroseconds(2);
  digitalwrite(pingpin, high);
  delaymicroseconds(5);
  digitalwrite(pingpin, low);
  //read echo
  pinmode(echopin, input);
  duration = pulsein(echopin, high);
    distance=(duration/2)*0.0341;
  serial.print("ping:  ");
  serial.println(distance);
}
void go(){
  digitalwrite(12, high);
  digitalwrite(9, low);
  digitalwrite(3, high);
  delay(600);
}
void turnleft(int t){
  digitalwrite (13, high);                             
  digitalwrite (8, low);
  digitalwrite (11, high);
  delay(t);
}
   
void turnright(int t){
  digitalwrite (13, low);                             
  digitalwrite (8, low);
  digitalwrite (11, high);
  delay(t);
}     
void forward(int t){
  digitalwrite(12, high);
  digitalwrite(9, low);
  digitalwrite(3, high);
  delay(600);
}
void backward(int t){
  digitalwrite (9, low);                             
  digitalwrite (12, low);
  digitalwrite(3, high);
  delay(t);
}
void stopmotors(){
  digitalwrite (9, high);                             
  digitalwrite (8, high);
  digitalwrite (3, high);
  digitalwrite (11, high);
  delay(600);
}     

char scan(){
  int leftscanval, centerscanval, rightscanval;
  char choice;
  //look left
  scanservo.write(30);
  delay(300);
  leftscanval = ping();
  //look right
  scanservo.write(150);
  delay(1000);
  rightscanval = ping();
  //center scan servo
  scanservo.write(88);

  if (leftscanval>rightscanval && leftscanval>centerscanval){
    choice = 'l';
  }
  else if (rightscanval>leftscanval && rightscanval>centerscanval){
    choice = 'r';
  }
  else if (rightscanval<30 && leftscanval<30 && centerscanval<30){
    choice = 'b';
  }
  else{
    choice = 's';
  }
  serial.print("choice:  ");
  serial.println(choice);
  return choice;
}

works alright....the problem is, moves fast...
so when try , set set using  "  analogwrite(3, 123);  in place of digitalwrite(3,high); example make beeping noises not sound healthy  .
i guess i'm not using pwm correctly. can see error?

please poor robot become best can be 

do think possible answer question without knowing hardware you're using , how connected?

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