Romeo v2 and robot chassis rp5-ch02

Hi everybody
I've got a problem with my romeo v2 and the rp5. I've connected everything and after I've uploaded a small sketch to check the engines ,nothing happends, just that irritating sound coming from both engines of rp5. I have no idea what cause the problem ??? :(.
Rp5 and romeo v2 is powered with 6 x AA 1,5v
The truth is I'm new to arduino and this is my first robot which I've decided to built.

Could someone help me please ?????

Thank you very much Greg

my sketch I've uploaded

//Standard PWM DC control
int E1 = 5; //M1 Speed Control
int E2 = 6; //M2 Speed Control
int M1 = 4; //M1 Direction Control
int M2 = 7; //M1 Direction Control

void advance(char a,char b) //Move forward
{
analogWrite (E1,a); //PWM Speed Control
digitalWrite(M1,HIGH);
analogWrite (E2,b);
digitalWrite(M2,HIGH);
}

void setup()
{
pinMode(13, OUTPUT);
}
void loop()
{
advance (20,20); //move forward
}