Arduino + UltraSensor - Serial Monitor outputs garbage
Check your serial monitor baud rate. This is definitely caused by your serial monitor being set to a different baud rate than the 9600 you specified in the program. 

If it had anything to do with the sensor than this line would be printed properly Serial.print("Distance: ");

Once you change the serial monitor baud rate then try running this program, to verify that it is set properly:

void setup() {
  Serial.begin(9600);
}

void loop() {
  Serial.println("Hi There!");
}


If that prints "Hi There!" then the program your serial monitor is set up properly.