Adobe Audition - Why am I hearing myself? And how do I turn it off!

Need a little more information here. Are you hearing yourself directly or with a slight delay? If you are hearing yourself with a delay, that means that Audition is in active monitor mode, and that the orange 'I' button to the right of the Record Enable button is lit. Click on that to stop it. If it's not this, then the issue is with the monitoring on your sound device, and since we don't know what that is, we can't help - but most allow a direct through monitoring option, and you can control the level of that using the device controls.