Arduino obstacle-avoiding car
I expect the &quot;beep&quot; comes from one of the motor, or maybe the servo.
9 volt batteries cannot deliver a lot of current.  Many DC motors and servos need more current than a 9V battery can supply.
You need a battery with the correct voltage and current rating for your motors and the servo.

I expect the Arduino tries to drive one or more of the motors (or the servo) - this causes the beep.  The Arduino drives the motors with a pulse width modulation (PWM) signal.  At each pulse, the motor tries to turn, but the battery can't deliver enough current to turn the motor.  The motor then just vibrates slightly in reaction to the pulses.
The servo would similarly cause a beep when the current is too low.
It beeps, pauses, and repeats because the load from the motor(s) causes the battery voltage to drop.  The low voltage causes the Arduino to restart.  Arduinos take a couple of seconds to start up.  It goes start, pause, try to move, battery voltage drops, Arduino resets, start, etc.  Repeat until the battery is totally dead.