You cant really tell which side it comes from. Its so high pitch you can barelly even hear it.

 

there is a way to locate it. If you have a passenger or you ride as one then take a rubber hose and hold one end to your ear and then move the other end around intill you hear the sound you will find the noise. you may have to insert a funnel in the hose to pick up more sound. it may be a fuel pump